diff --git a/pkg/apis/kubeflow.org/v1/mpi_defaults.go b/pkg/apis/kubeflow.org/v1/mpi_defaults.go
index 47d41ec748..df5c2e4807 100644
--- a/pkg/apis/kubeflow.org/v1/mpi_defaults.go
+++ b/pkg/apis/kubeflow.org/v1/mpi_defaults.go
@@ -32,9 +32,11 @@ func SetDefaults_MPIJob(mpiJob *MPIJob) {
 		mpiJob.Spec.RunPolicy.CleanPodPolicy = &none
 	}
 
-	// set default to Launcher
-	setDefaultRestartPolicy(mpiJob.Spec.MPIReplicaSpecs[MPIJobReplicaTypeLauncher], MPIJobDefaultRestartPolicy)
+	// Set default replicas
+	setDefaultReplicas(mpiJob.Spec.MPIReplicaSpecs[MPIJobReplicaTypeLauncher], 1)
+	setDefaultReplicas(mpiJob.Spec.MPIReplicaSpecs[MPIJobReplicaTypeWorker], 0)
 
-	// set default to Worker
+	// Set default restartPolicy
+	setDefaultRestartPolicy(mpiJob.Spec.MPIReplicaSpecs[MPIJobReplicaTypeLauncher], MPIJobDefaultRestartPolicy)
 	setDefaultRestartPolicy(mpiJob.Spec.MPIReplicaSpecs[MPIJobReplicaTypeWorker], MPIJobDefaultRestartPolicy)
 }
diff --git a/pkg/apis/kubeflow.org/v1/mpi_defaults_test.go b/pkg/apis/kubeflow.org/v1/mpi_defaults_test.go
new file mode 100644
index 0000000000..f4818541bf
--- /dev/null
+++ b/pkg/apis/kubeflow.org/v1/mpi_defaults_test.go
@@ -0,0 +1,175 @@
+package v1
+
+import (
+	"reflect"
+	"testing"
+
+	corev1 "k8s.io/api/core/v1"
+	"k8s.io/utils/pointer"
+
+	commonv1 "github.com/kubeflow/common/pkg/apis/common/v1"
+	"github.com/kubeflow/common/pkg/util"
+)
+
+func expectedMPIJob(cleanPodPolicy commonv1.CleanPodPolicy, restartPolicy commonv1.RestartPolicy) *MPIJob {
+	return &MPIJob{
+		Spec: MPIJobSpec{
+			CleanPodPolicy: &cleanPodPolicy,
+			RunPolicy: commonv1.RunPolicy{
+				CleanPodPolicy: &cleanPodPolicy,
+			},
+			MPIReplicaSpecs: map[commonv1.ReplicaType]*commonv1.ReplicaSpec{
+				MPIJobReplicaTypeLauncher: {
+					Replicas:      pointer.Int32(1),
+					RestartPolicy: restartPolicy,
+					Template: corev1.PodTemplateSpec{
+						Spec: corev1.PodSpec{
+							Containers: []corev1.Container{
+								{
+									Name:  MPIJobDefaultContainerName,
+									Image: testImage,
+								},
+							},
+						},
+					},
+				},
+				MPIJobReplicaTypeWorker: {
+					Replicas:      pointer.Int32(0),
+					RestartPolicy: restartPolicy,
+					Template: corev1.PodTemplateSpec{
+						Spec: corev1.PodSpec{
+							Containers: []corev1.Container{
+								{
+									Name:  MPIJobDefaultContainerName,
+									Image: testImage,
+								},
+							},
+						},
+					},
+				},
+			},
+		},
+	}
+}
+
+func TestSetDefaults_MPIJob(t *testing.T) {
+	customRestartPolicy := commonv1.RestartPolicyAlways
+	customCleanPodPolicy := commonv1.CleanPodPolicyRunning
+
+	testCases := map[string]struct {
+		original *MPIJob
+		expected *MPIJob
+	}{
+		"set default replicas": {
+			original: &MPIJob{
+				Spec: MPIJobSpec{
+					CleanPodPolicy: &customCleanPodPolicy,
+					RunPolicy: commonv1.RunPolicy{
+						CleanPodPolicy: &customCleanPodPolicy,
+					},
+					MPIReplicaSpecs: map[commonv1.ReplicaType]*commonv1.ReplicaSpec{
+						MPIJobReplicaTypeLauncher: {
+							RestartPolicy: customRestartPolicy,
+							Template: corev1.PodTemplateSpec{
+								Spec: corev1.PodSpec{
+									Containers: []corev1.Container{
+										{
+											Name:  MPIJobDefaultContainerName,
+											Image: testImage,
+										},
+									},
+								},
+							},
+						},
+						MPIJobReplicaTypeWorker: {
+							RestartPolicy: customRestartPolicy,
+							Template: corev1.PodTemplateSpec{
+								Spec: corev1.PodSpec{
+									Containers: []corev1.Container{
+										{
+											Name:  MPIJobDefaultContainerName,
+											Image: testImage,
+										},
+									},
+								},
+							},
+						},
+					},
+				},
+			},
+			expected: expectedMPIJob(customCleanPodPolicy, customRestartPolicy),
+		},
+		"set default clean pod policy": {
+			original: &MPIJob{
+				Spec: MPIJobSpec{
+					MPIReplicaSpecs: map[commonv1.ReplicaType]*commonv1.ReplicaSpec{
+						MPIJobReplicaTypeLauncher: {
+							Template: corev1.PodTemplateSpec{
+								Spec: corev1.PodSpec{
+									Containers: []corev1.Container{
+										{
+											Name:  MPIJobDefaultContainerName,
+											Image: testImage,
+										},
+									},
+								},
+							},
+						},
+						MPIJobReplicaTypeWorker: {
+							Template: corev1.PodTemplateSpec{
+								Spec: corev1.PodSpec{
+									Containers: []corev1.Container{
+										{
+											Name:  MPIJobDefaultContainerName,
+											Image: testImage,
+										},
+									},
+								},
+							},
+						},
+					},
+				},
+			},
+			expected: expectedMPIJob(commonv1.CleanPodPolicyNone, MPIJobDefaultRestartPolicy),
+		},
+		"set default restart policy": {
+			original: &MPIJob{
+				Spec: MPIJobSpec{
+					MPIReplicaSpecs: map[commonv1.ReplicaType]*commonv1.ReplicaSpec{
+						MPIJobReplicaTypeLauncher: {
+							Template: corev1.PodTemplateSpec{
+								Spec: corev1.PodSpec{
+									Containers: []corev1.Container{
+										{
+											Name:  MPIJobDefaultContainerName,
+											Image: testImage,
+										},
+									},
+								},
+							},
+						},
+						MPIJobReplicaTypeWorker: {
+							Template: corev1.PodTemplateSpec{
+								Spec: corev1.PodSpec{
+									Containers: []corev1.Container{
+										{
+											Name:  MPIJobDefaultContainerName,
+											Image: testImage,
+										},
+									},
+								},
+							},
+						},
+					},
+				},
+			},
+			expected: expectedMPIJob(commonv1.CleanPodPolicyNone, MPIJobDefaultRestartPolicy),
+		},
+	}
+	for name, tc := range testCases {
+		SetDefaults_MPIJob(tc.original)
+		if !reflect.DeepEqual(tc.original, tc.expected) {
+			t.Errorf("%s: Want\n%v; Got\n %v", name, util.Pformat(tc.expected), util.Pformat(tc.original))
+		}
+	}
+}