diff --git a/pkg/app/pipedv1/plugin/kubernetes/provider/kubernetes.go b/pkg/app/pipedv1/plugin/kubernetes/provider/kubernetes.go
new file mode 100644
index 0000000000..04d14d2cd1
--- /dev/null
+++ b/pkg/app/pipedv1/plugin/kubernetes/provider/kubernetes.go
@@ -0,0 +1,19 @@
+// Copyright 2024 The PipeCD Authors.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//	http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package provider
+
+const (
+	AnnotationOrder = "pipecd.dev/order" // The order number of resource used to sort them before using.
+)
diff --git a/pkg/app/pipedv1/plugin/kubernetes/provider/loader.go b/pkg/app/pipedv1/plugin/kubernetes/provider/loader.go
index aeb59eb1e0..87511789e8 100644
--- a/pkg/app/pipedv1/plugin/kubernetes/provider/loader.go
+++ b/pkg/app/pipedv1/plugin/kubernetes/provider/loader.go
@@ -14,6 +14,172 @@
 
 package provider
 
+import (
+	"errors"
+	"fmt"
+	"io/fs"
+	"os"
+	"path/filepath"
+	"slices"
+	"strconv"
+	"strings"
+
+	"k8s.io/apimachinery/pkg/apis/meta/v1/unstructured"
+	"sigs.k8s.io/yaml"
+
+	"github.com/pipe-cd/pipecd/pkg/model"
+)
+
+type TemplatingMethod string
+
+const (
+	TemplatingMethodHelm      TemplatingMethod = "helm"
+	TemplatingMethodKustomize TemplatingMethod = "kustomize"
+	TemplatingMethodNone      TemplatingMethod = "none"
+)
+
 type LoaderInput struct {
+	AppDir         string
+	ConfigFilename string
+	Manifests      []string
+
+	Namespace        string
+	TemplatingMethod TemplatingMethod
+
 	// TODO: define fields for LoaderInput.
 }
+
+type Loader struct {
+}
+
+func (l *Loader) LoadManifests(input LoaderInput) (manifests []Manifest, err error) {
+	defer func() {
+		// Override namespace if set because ParseManifests does not parse it
+		// if namespace is not explicitly specified in the manifests.
+		setNamespace(manifests, input.Namespace)
+		sortManifests(manifests)
+	}()
+
+	switch input.TemplatingMethod {
+	case TemplatingMethodHelm:
+		return nil, errors.New("not implemented yet")
+	case TemplatingMethodKustomize:
+		return nil, errors.New("not implemented yet")
+	case TemplatingMethodNone:
+		return LoadPlainYAMLManifests(input.AppDir, input.Manifests, input.ConfigFilename)
+	default:
+		return nil, fmt.Errorf("unsupported templating method %s", input.TemplatingMethod)
+	}
+}
+
+func setNamespace(manifests []Manifest, namespace string) {
+	if namespace == "" {
+		return
+	}
+	for i := range manifests {
+		manifests[i].Key.Namespace = namespace
+	}
+}
+
+func sortManifests(manifests []Manifest) {
+	if len(manifests) < 2 {
+		return
+	}
+
+	slices.SortFunc(manifests, func(a, b Manifest) int {
+		iAns := a.Body.GetAnnotations()
+		// Ignore the converting error since it is not so much important.
+		iIndex, _ := strconv.Atoi(iAns[AnnotationOrder])
+
+		jAns := b.Body.GetAnnotations()
+		// Ignore the converting error since it is not so much important.
+		jIndex, _ := strconv.Atoi(jAns[AnnotationOrder])
+
+		return iIndex - jIndex
+	})
+}
+
+func LoadPlainYAMLManifests(dir string, names []string, configFilename string) ([]Manifest, error) {
+	// If no name was specified we have to walk the app directory to collect the manifest list.
+	if len(names) == 0 {
+		err := filepath.WalkDir(dir, func(path string, d fs.DirEntry, err error) error {
+			if err != nil {
+				return err
+			}
+			if path == dir {
+				return nil
+			}
+			if d.IsDir() {
+				return fs.SkipDir
+			}
+			if ext := filepath.Ext(d.Name()); ext != ".yaml" && ext != ".yml" && ext != ".json" {
+				return nil
+			}
+			if model.IsApplicationConfigFile(d.Name()) {
+				// MEMO: can we remove this check because we have configFilename?
+				return nil
+			}
+			if d.Name() == configFilename {
+				return nil
+			}
+			names = append(names, d.Name())
+			return nil
+		})
+		if err != nil {
+			return nil, err
+		}
+	}
+
+	manifests := make([]Manifest, 0, len(names))
+	for _, name := range names {
+		path := filepath.Join(dir, name)
+		ms, err := LoadManifestsFromYAMLFile(path)
+		if err != nil {
+			return nil, fmt.Errorf("failed to load manifest at %s (%w)", path, err)
+		}
+		manifests = append(manifests, ms...)
+	}
+
+	return manifests, nil
+}
+
+// LoadManifestsFromYAMLFile loads the manifests from the given file.
+func LoadManifestsFromYAMLFile(path string) ([]Manifest, error) {
+	data, err := os.ReadFile(path)
+	if err != nil {
+		return nil, err
+	}
+	return ParseManifests(string(data))
+}
+
+// ParseManifests parses the given data and returns a list of Manifest.
+func ParseManifests(data string) ([]Manifest, error) {
+	const separator = "\n---"
+	var (
+		parts     = strings.Split(data, separator)
+		manifests = make([]Manifest, 0, len(parts))
+	)
+
+	for i, part := range parts {
+		// Ignore all the cases where no content between separator.
+		if len(strings.TrimSpace(part)) == 0 {
+			continue
+		}
+		// Append new line which trim by document separator.
+		if i != len(parts)-1 {
+			part += "\n"
+		}
+		var obj unstructured.Unstructured
+		if err := yaml.Unmarshal([]byte(part), &obj); err != nil {
+			return nil, err
+		}
+		if len(obj.Object) == 0 {
+			continue
+		}
+		manifests = append(manifests, Manifest{
+			Key:  MakeResourceKey(&obj),
+			Body: &obj,
+		})
+	}
+	return manifests, nil
+}
diff --git a/pkg/app/pipedv1/plugin/kubernetes/provider/loader_test.go b/pkg/app/pipedv1/plugin/kubernetes/provider/loader_test.go
new file mode 100644
index 0000000000..2f17402902
--- /dev/null
+++ b/pkg/app/pipedv1/plugin/kubernetes/provider/loader_test.go
@@ -0,0 +1,339 @@
+// Copyright 2024 The PipeCD Authors.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//  http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package provider
+
+import (
+	"os"
+	"path/filepath"
+	"reflect"
+	"testing"
+
+	"github.com/stretchr/testify/assert"
+	"github.com/stretchr/testify/require"
+	"k8s.io/apimachinery/pkg/apis/meta/v1/unstructured"
+)
+
+func TestParseManifests(t *testing.T) {
+	tests := []struct {
+		name    string
+		data    string
+		want    []Manifest
+		wantErr bool
+	}{
+		{
+			name: "single manifest",
+			data: `
+apiVersion: v1
+kind: ConfigMap
+metadata:
+  name: test-config
+`,
+			want: []Manifest{
+				{
+					Key: ResourceKey{
+						APIVersion: "v1",
+						Kind:       "ConfigMap",
+						Name:       "test-config",
+					},
+					Body: &unstructured.Unstructured{
+						Object: map[string]interface{}{
+							"apiVersion": "v1",
+							"kind":       "ConfigMap",
+							"metadata": map[string]interface{}{
+								"name": "test-config",
+							},
+						},
+					},
+				},
+			},
+			wantErr: false,
+		},
+		{
+			name: "multiple manifests",
+			data: `
+apiVersion: v1
+kind: ConfigMap
+metadata:
+  name: test-config
+---
+apiVersion: v1
+kind: Service
+metadata:
+  name: test-service
+`,
+			want: []Manifest{
+				{
+					Key: ResourceKey{
+						APIVersion: "v1",
+						Kind:       "ConfigMap",
+						Name:       "test-config",
+					},
+					Body: &unstructured.Unstructured{
+						Object: map[string]interface{}{
+							"apiVersion": "v1",
+							"kind":       "ConfigMap",
+							"metadata": map[string]interface{}{
+								"name": "test-config",
+							},
+						},
+					},
+				},
+				{
+					Key: ResourceKey{
+						APIVersion: "v1",
+						Kind:       "Service",
+						Name:       "test-service",
+					},
+					Body: &unstructured.Unstructured{
+						Object: map[string]interface{}{
+							"apiVersion": "v1",
+							"kind":       "Service",
+							"metadata": map[string]interface{}{
+								"name": "test-service",
+							},
+						},
+					},
+				},
+			},
+			wantErr: false,
+		},
+		{
+			name: "invalid manifest",
+			data: `
+apiVersion: v1
+kind: ConfigMap
+metadata:
+  name: test-config
+---
+invalid yaml
+`,
+			want:    nil,
+			wantErr: true,
+		},
+		{
+			name: "empty manifest",
+			data: `
+---
+`,
+			want:    []Manifest{},
+			wantErr: false,
+		},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			got, err := ParseManifests(tt.data)
+			if (err != nil) != tt.wantErr {
+				t.Errorf("ParseManifests() error = %v, wantErr %v", err, tt.wantErr)
+				return
+			}
+			if !reflect.DeepEqual(got, tt.want) {
+				t.Errorf("ParseManifests() got = %v, want %v", got, tt.want)
+			}
+		})
+	}
+}
+
+func TestLoadPlainYAMLManifests(t *testing.T) {
+	t.Parallel()
+
+	tests := []struct {
+		name           string
+		dir            string
+		names          []string
+		configFilename string
+		setup          func(dir string) error
+		want           []Manifest
+		wantErr        bool
+	}{
+		{
+			name:           "load single manifest",
+			dir:            "testdata/single",
+			names:          []string{"configmap.yaml"},
+			configFilename: "pipecd-config.yaml",
+			setup: func(dir string) error {
+				return os.WriteFile(filepath.Join(dir, "configmap.yaml"), []byte(`
+apiVersion: v1
+kind: ConfigMap
+metadata:
+  name: test-config
+`), 0644)
+			},
+			want: []Manifest{
+				{
+					Key: ResourceKey{
+						APIVersion: "v1",
+						Kind:       "ConfigMap",
+						Name:       "test-config",
+					},
+					Body: &unstructured.Unstructured{
+						Object: map[string]interface{}{
+							"apiVersion": "v1",
+							"kind":       "ConfigMap",
+							"metadata": map[string]interface{}{
+								"name": "test-config",
+							},
+						},
+					},
+				},
+			},
+			wantErr: false,
+		},
+		{
+			name:           "ignore config file",
+			dir:            "testdata/ignore-config",
+			names:          []string{},
+			configFilename: "pipecd-config.yaml",
+			setup: func(dir string) error {
+				// Place dummy files to ensure the loader ignores them.
+				if err := os.WriteFile(filepath.Join(dir, "pipecd-config.yaml"), []byte(`
+apiVersion: v1
+kind: ConfigMap
+metadata:
+  name: pipecd-config
+`), 0644); err != nil {
+					return err
+				}
+				return os.WriteFile(filepath.Join(dir, "service.yaml"), []byte(`
+apiVersion: v1
+kind: Service
+metadata:
+  name: test-service
+`), 0644)
+			},
+			want: []Manifest{
+				{
+					Key: ResourceKey{
+						APIVersion: "v1",
+						Kind:       "Service",
+						Name:       "test-service",
+					},
+					Body: &unstructured.Unstructured{
+						Object: map[string]interface{}{
+							"apiVersion": "v1",
+							"kind":       "Service",
+							"metadata": map[string]interface{}{
+								"name": "test-service",
+							},
+						},
+					},
+				},
+			},
+			wantErr: false,
+		},
+		{
+			name:           "load multiple manifests",
+			dir:            "testdata/multiple",
+			names:          []string{"configmap.yaml", "service.yaml"},
+			configFilename: "pipecd-config.yaml",
+			setup: func(dir string) error {
+				if err := os.WriteFile(filepath.Join(dir, "configmap.yaml"), []byte(`
+apiVersion: v1
+kind: ConfigMap
+metadata:
+  name: test-config
+`), 0644); err != nil {
+					return err
+				}
+				return os.WriteFile(filepath.Join(dir, "service.yaml"), []byte(`
+apiVersion: v1
+kind: Service
+metadata:
+  name: test-service
+`), 0644)
+			},
+			want: []Manifest{
+				{
+					Key: ResourceKey{
+						APIVersion: "v1",
+						Kind:       "ConfigMap",
+						Name:       "test-config",
+					},
+					Body: &unstructured.Unstructured{
+						Object: map[string]interface{}{
+							"apiVersion": "v1",
+							"kind":       "ConfigMap",
+							"metadata": map[string]interface{}{
+								"name": "test-config",
+							},
+						},
+					},
+				},
+				{
+					Key: ResourceKey{
+						APIVersion: "v1",
+						Kind:       "Service",
+						Name:       "test-service",
+					},
+					Body: &unstructured.Unstructured{
+						Object: map[string]interface{}{
+							"apiVersion": "v1",
+							"kind":       "Service",
+							"metadata": map[string]interface{}{
+								"name": "test-service",
+							},
+						},
+					},
+				},
+			},
+			wantErr: false,
+		},
+		{
+			name:           "invalid manifest",
+			dir:            "testdata/invalid",
+			names:          []string{"invalid.yaml"},
+			configFilename: "pipecd-config.yaml",
+			setup: func(dir string) error {
+				return os.WriteFile(filepath.Join(dir, "invalid.yaml"), []byte(`
+invalid yaml content
+`), 0644)
+			},
+			want:    nil,
+			wantErr: true,
+		},
+		{
+			name:           "no manifests",
+			dir:            "testdata/empty",
+			names:          []string{},
+			configFilename: "pipecd-config.yaml",
+			setup: func(dir string) error {
+				return nil
+			},
+			want:    []Manifest{},
+			wantErr: false,
+		},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			t.Parallel()
+
+			dir := filepath.Join(t.TempDir(), tt.dir)
+			require.NoError(t, os.MkdirAll(dir, 0755))
+
+			if tt.setup != nil {
+				require.NoError(t, tt.setup(dir))
+			}
+
+			got, err := LoadPlainYAMLManifests(dir, tt.names, tt.configFilename)
+			if tt.wantErr {
+				require.Error(t, err)
+			} else {
+				require.NoError(t, err)
+			}
+			assert.ElementsMatch(t, tt.want, got)
+		})
+	}
+}
diff --git a/pkg/app/pipedv1/plugin/kubernetes/provider/manifest.go b/pkg/app/pipedv1/plugin/kubernetes/provider/manifest.go
index 9856d60558..93b3cc7b9e 100644
--- a/pkg/app/pipedv1/plugin/kubernetes/provider/manifest.go
+++ b/pkg/app/pipedv1/plugin/kubernetes/provider/manifest.go
@@ -18,7 +18,7 @@ import "k8s.io/apimachinery/pkg/apis/meta/v1/unstructured"
 
 // Manifest represents a Kubernetes resource manifest.
 type Manifest struct {
-	// TODO: define ResourceKey and add as a field here.
+	Key ResourceKey
 	Body *unstructured.Unstructured
 }
 
diff --git a/pkg/app/pipedv1/plugin/kubernetes/provider/resource.go b/pkg/app/pipedv1/plugin/kubernetes/provider/resource.go
index 35d95aff8f..3337e1d4d6 100644
--- a/pkg/app/pipedv1/plugin/kubernetes/provider/resource.go
+++ b/pkg/app/pipedv1/plugin/kubernetes/provider/resource.go
@@ -14,4 +14,37 @@
 
 package provider
 
+import (
+	"fmt"
+
+	"k8s.io/apimachinery/pkg/apis/meta/v1/unstructured"
+)
+
+
+
 const KindDeployment = "Deployment"
+
+type ResourceKey struct {
+	APIVersion string
+	Kind      string
+	Namespace string
+	Name      string
+}
+
+func (k ResourceKey) String() string {
+	return fmt.Sprintf("%s:%s:%s:%s", k.APIVersion, k.Kind, k.Namespace, k.Name)
+}
+
+func (k ResourceKey) ReadableString() string {
+	return fmt.Sprintf("name=%q, kind=%q, namespace=%q, apiVersion=%q", k.Name, k.Kind, k.Namespace, k.APIVersion)
+}
+
+func MakeResourceKey(obj *unstructured.Unstructured) ResourceKey {
+	k := ResourceKey{
+		APIVersion: obj.GetAPIVersion(),
+		Kind:       obj.GetKind(),
+		Namespace:  obj.GetNamespace(),
+		Name:       obj.GetName(),
+	}
+	return k
+}