diff --git a/pkg/app/pipedv1/plugin/kubernetes_multicluster/config/application.go b/pkg/app/pipedv1/plugin/kubernetes_multicluster/config/application.go
index ca51727db0..a76d92317e 100644
--- a/pkg/app/pipedv1/plugin/kubernetes_multicluster/config/application.go
+++ b/pkg/app/pipedv1/plugin/kubernetes_multicluster/config/application.go
@@ -78,7 +78,14 @@ func (s *KubernetesApplicationSpec) UnmarshalJSON(data []byte) error {
 }
 
 func (s *KubernetesApplicationSpec) Validate() error {
-	// TODO: Validate KubernetesApplicationSpec fields.
+	if s.Input.HelmChart != nil && len(s.Input.KustomizeOptions) > 0 {
+		return errors.New("helmChart and kustomizeOptions are mutually exclusive")
+	}
+	for i, mt := range s.Input.MultiTargets {
+		if mt.Target.Name == "" {
+			return fmt.Errorf("multiTargets[%d].target.name must not be empty", i)
+		}
+	}
 	return nil
 }
 
diff --git a/pkg/app/pipedv1/plugin/kubernetes_multicluster/config/application_test.go b/pkg/app/pipedv1/plugin/kubernetes_multicluster/config/application_test.go
index 61e72fb01c..55b010d96f 100644
--- a/pkg/app/pipedv1/plugin/kubernetes_multicluster/config/application_test.go
+++ b/pkg/app/pipedv1/plugin/kubernetes_multicluster/config/application_test.go
@@ -97,3 +97,75 @@ func TestFindDeployTarget(t *testing.T) {
 		})
 	}
 }
+
+func TestKubernetesApplicationSpecValidate(t *testing.T) {
+	tests := []struct {
+		name        string
+		spec        KubernetesApplicationSpec
+		expectedErr string
+	}{
+		{
+			name: "valid empty spec",
+			spec: KubernetesApplicationSpec{},
+		},
+		{
+			name: "valid single multiTarget",
+			spec: KubernetesApplicationSpec{
+				Input: KubernetesDeploymentInput{
+					MultiTargets: []KubernetesMultiTarget{
+						{Target: KubernetesMultiTargetDeployTarget{Name: "cluster-us"}},
+					},
+				},
+			},
+		},
+		{
+			name: "multiTarget with empty name",
+			spec: KubernetesApplicationSpec{
+				Input: KubernetesDeploymentInput{
+					MultiTargets: []KubernetesMultiTarget{
+						{Target: KubernetesMultiTargetDeployTarget{Name: "cluster-us"}},
+						{Target: KubernetesMultiTargetDeployTarget{Name: ""}},
+					},
+				},
+			},
+			expectedErr: "multiTargets[1].target.name must not be empty",
+		},
+		{
+			name: "helmChart and kustomizeOptions are mutually exclusive",
+			spec: KubernetesApplicationSpec{
+				Input: KubernetesDeploymentInput{
+					HelmChart:        &InputHelmChart{Path: "./charts/myapp"},
+					KustomizeOptions: map[string]string{"enable-alpha-plugins": "true"},
+				},
+			},
+			expectedErr: "helmChart and kustomizeOptions are mutually exclusive",
+		},
+		{
+			name: "helmChart without kustomizeOptions is valid",
+			spec: KubernetesApplicationSpec{
+				Input: KubernetesDeploymentInput{
+					HelmChart: &InputHelmChart{Path: "./charts/myapp"},
+				},
+			},
+		},
+		{
+			name: "kustomizeOptions without helmChart is valid",
+			spec: KubernetesApplicationSpec{
+				Input: KubernetesDeploymentInput{
+					KustomizeOptions: map[string]string{"enable-alpha-plugins": "true"},
+				},
+			},
+		},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			err := tt.spec.Validate()
+			if tt.expectedErr != "" {
+				assert.EqualError(t, err, tt.expectedErr)
+			} else {
+				assert.NoError(t, err)
+			}
+		})
+	}
+}