diff --git a/Assets/VRM/UniVRM/Editor/Tests/UniVRMSerializeTests.cs b/Assets/VRM/UniVRM/Editor/Tests/UniVRMSerializeTests.cs
index b3d3362d9f..8fba75208c 100644
--- a/Assets/VRM/UniVRM/Editor/Tests/UniVRMSerializeTests.cs
+++ b/Assets/VRM/UniVRM/Editor/Tests/UniVRMSerializeTests.cs
@@ -617,6 +617,27 @@ public void SecondaryAnimationTest()
             Assert.AreEqual(json,json2);
         }
 
+        [Test]
+        public void ExtensionsTest()
+        {
+            var model = new glTF_VRM_extensions()
+            {
+                meta = null,
+                humanoid = null,
+                firstPerson = null,
+                blendShapeMaster = null,
+                secondaryAnimation = null,
+                materialProperties = null,
+            };
+
+            var c = new JsonSchemaValidationContext("")
+            {
+                EnableDiagnosisForNotRequiredFields = true,
+            };
+            var json2 = JsonSchema.FromType<glTF_VRM_extensions>().Serialize(model, c);
+            Assert.AreEqual(@"{""exporterVersion"":""UniVRM-0.50"",""specVersion"":""0.0""}",json2);
+        }
+
         // TODO: Move to another suitable location
         T deserialize<T>(string json)
         {
diff --git a/Assets/VRM/UniVRM/Scripts/Format/VRMFormat.cs b/Assets/VRM/UniVRM/Scripts/Format/VRMFormat.cs
index 348c37b5b3..501328e152 100644
--- a/Assets/VRM/UniVRM/Scripts/Format/VRMFormat.cs
+++ b/Assets/VRM/UniVRM/Scripts/Format/VRMFormat.cs
@@ -37,6 +37,9 @@ public static string ExtensionName
         [JsonSchema(Description = @"Version of exporter that vrm created. " + VRMVersion.VRM_VERSION)]
         public string exporterVersion = "UniVRM-" + VRMVersion.VERSION;
 
+        [JsonSchema(Description = @"The VRM specification version that this extension uses")]
+        public string specVersion  = VRMSpecVersion.Version;
+
         public glTF_VRM_Meta meta = new glTF_VRM_Meta();
         public glTF_VRM_Humanoid humanoid = new glTF_VRM_Humanoid();
         public glTF_VRM_Firstperson firstPerson = new glTF_VRM_Firstperson();
@@ -47,6 +50,7 @@ public static string ExtensionName
         protected override void SerializeMembers(GLTFJsonFormatter f)
         {
             f.KeyValue(() => exporterVersion);
+            f.KeyValue(() => specVersion);
             f.Key("meta"); f.GLTFValue(meta);
             f.Key("humanoid"); f.GLTFValue(humanoid);
             f.Key("firstPerson"); f.GLTFValue(firstPerson);
diff --git a/Assets/VRM/UniVRM/Scripts/Format/VRMSpecVersion.cs b/Assets/VRM/UniVRM/Scripts/Format/VRMSpecVersion.cs
new file mode 100644
index 0000000000..98ece65e76
--- /dev/null
+++ b/Assets/VRM/UniVRM/Scripts/Format/VRMSpecVersion.cs
@@ -0,0 +1,18 @@
+using System;
+
+namespace VRM
+{
+    public class VRMSpecVersion
+    {
+        public const int Major = 0;
+        public const int Minor = 0;
+
+        public static string Version
+        {
+            get
+            {
+                return String.Format("{0}.{1}", Major, Minor);
+            }
+        }
+    }
+}
diff --git a/Assets/VRM/UniVRM/Scripts/Format/VRMSpecVersion.cs.meta b/Assets/VRM/UniVRM/Scripts/Format/VRMSpecVersion.cs.meta
new file mode 100644
index 0000000000..7c160b301b
--- /dev/null
+++ b/Assets/VRM/UniVRM/Scripts/Format/VRMSpecVersion.cs.meta
@@ -0,0 +1,3 @@
+fileFormatVersion: 2
+guid: 3c5b8467d0154d6da78a74ecae5f85e7
+timeCreated: 1549016543
\ No newline at end of file