diff --git a/docs/Activity.md b/docs/Activity.md
index 87e055a..b471fd9 100644
--- a/docs/Activity.md
+++ b/docs/Activity.md
@@ -11,8 +11,40 @@ Name | Type | Description | Notes
 **created** | [**Date**](Date.md) |  |  [optional]
 **id** | **Long** |  |  [optional]
 **isPrivate** | **Boolean** |  |  [optional]
-**opType** | **String** |  |  [optional]
+**opType** | [**OpTypeEnum**](#OpTypeEnum) | the type of action |  [optional]
 **refName** | **String** |  |  [optional]
 **repo** | [**Repository**](Repository.md) |  |  [optional]
 **repoId** | **Long** |  |  [optional]
 **userId** | **Long** |  |  [optional]
+
+<a name="OpTypeEnum"></a>
+## Enum: OpTypeEnum
+Name | Value
+---- | -----
+CREATE_REPO | &quot;create_repo&quot;
+RENAME_REPO | &quot;rename_repo&quot;
+STAR_REPO | &quot;star_repo&quot;
+WATCH_REPO | &quot;watch_repo&quot;
+COMMIT_REPO | &quot;commit_repo&quot;
+CREATE_ISSUE | &quot;create_issue&quot;
+CREATE_PULL_REQUEST | &quot;create_pull_request&quot;
+TRANSFER_REPO | &quot;transfer_repo&quot;
+PUSH_TAG | &quot;push_tag&quot;
+COMMENT_ISSUE | &quot;comment_issue&quot;
+MERGE_PULL_REQUEST | &quot;merge_pull_request&quot;
+CLOSE_ISSUE | &quot;close_issue&quot;
+REOPEN_ISSUE | &quot;reopen_issue&quot;
+CLOSE_PULL_REQUEST | &quot;close_pull_request&quot;
+REOPEN_PULL_REQUEST | &quot;reopen_pull_request&quot;
+DELETE_TAG | &quot;delete_tag&quot;
+DELETE_BRANCH | &quot;delete_branch&quot;
+MIRROR_SYNC_PUSH | &quot;mirror_sync_push&quot;
+MIRROR_SYNC_CREATE | &quot;mirror_sync_create&quot;
+MIRROR_SYNC_DELETE | &quot;mirror_sync_delete&quot;
+APPROVE_PULL_REQUEST | &quot;approve_pull_request&quot;
+REJECT_PULL_REQUEST | &quot;reject_pull_request&quot;
+COMMENT_PULL | &quot;comment_pull&quot;
+PUBLISH_RELEASE | &quot;publish_release&quot;
+PULL_REVIEW_DISMISSED | &quot;pull_review_dismissed&quot;
+PULL_REQUEST_READY_FOR_REVIEW | &quot;pull_request_ready_for_review&quot;
+AUTO_MERGE_PULL_REQUEST | &quot;auto_merge_pull_request&quot;
diff --git a/src/main/java/org/gitnex/tea4j/v2/models/Activity.java b/src/main/java/org/gitnex/tea4j/v2/models/Activity.java
index 5d5bfb4..f903247 100644
--- a/src/main/java/org/gitnex/tea4j/v2/models/Activity.java
+++ b/src/main/java/org/gitnex/tea4j/v2/models/Activity.java
@@ -12,8 +12,13 @@
 
 package org.gitnex.tea4j.v2.models;
 
+import com.google.gson.TypeAdapter;
+import com.google.gson.annotations.JsonAdapter;
 import com.google.gson.annotations.SerializedName;
+import com.google.gson.stream.JsonReader;
+import com.google.gson.stream.JsonWriter;
 import io.swagger.v3.oas.annotations.media.Schema;
+import java.io.IOException;
 import java.io.Serializable;
 import java.util.Date;
 import java.util.Objects;
@@ -46,8 +51,78 @@ public class Activity implements Serializable {
   @SerializedName("is_private")
   private Boolean isPrivate = null;
 
+  /** the type of action */
+  @JsonAdapter(OpTypeEnum.Adapter.class)
+  public enum OpTypeEnum {
+    CREATE_REPO("create_repo"),
+    RENAME_REPO("rename_repo"),
+    STAR_REPO("star_repo"),
+    WATCH_REPO("watch_repo"),
+    COMMIT_REPO("commit_repo"),
+    CREATE_ISSUE("create_issue"),
+    CREATE_PULL_REQUEST("create_pull_request"),
+    TRANSFER_REPO("transfer_repo"),
+    PUSH_TAG("push_tag"),
+    COMMENT_ISSUE("comment_issue"),
+    MERGE_PULL_REQUEST("merge_pull_request"),
+    CLOSE_ISSUE("close_issue"),
+    REOPEN_ISSUE("reopen_issue"),
+    CLOSE_PULL_REQUEST("close_pull_request"),
+    REOPEN_PULL_REQUEST("reopen_pull_request"),
+    DELETE_TAG("delete_tag"),
+    DELETE_BRANCH("delete_branch"),
+    MIRROR_SYNC_PUSH("mirror_sync_push"),
+    MIRROR_SYNC_CREATE("mirror_sync_create"),
+    MIRROR_SYNC_DELETE("mirror_sync_delete"),
+    APPROVE_PULL_REQUEST("approve_pull_request"),
+    REJECT_PULL_REQUEST("reject_pull_request"),
+    COMMENT_PULL("comment_pull"),
+    PUBLISH_RELEASE("publish_release"),
+    PULL_REVIEW_DISMISSED("pull_review_dismissed"),
+    PULL_REQUEST_READY_FOR_REVIEW("pull_request_ready_for_review"),
+    AUTO_MERGE_PULL_REQUEST("auto_merge_pull_request");
+
+    private String value;
+
+    OpTypeEnum(String value) {
+      this.value = value;
+    }
+
+    public String getValue() {
+      return value;
+    }
+
+    @Override
+    public String toString() {
+      return String.valueOf(value);
+    }
+
+    public static OpTypeEnum fromValue(String input) {
+      for (OpTypeEnum b : OpTypeEnum.values()) {
+        if (b.value.equals(input)) {
+          return b;
+        }
+      }
+      return null;
+    }
+
+    public static class Adapter extends TypeAdapter<OpTypeEnum> {
+      @Override
+      public void write(final JsonWriter jsonWriter, final OpTypeEnum enumeration)
+          throws IOException {
+        jsonWriter.value(String.valueOf(enumeration.getValue()));
+      }
+
+      @Override
+      public OpTypeEnum read(final JsonReader jsonReader) throws IOException {
+        Object value = jsonReader.nextString();
+        return OpTypeEnum.fromValue((String) (value));
+      }
+    }
+  }
+
   @SerializedName("op_type")
-  private String opType = null;
+  private OpTypeEnum opType = null;
 
   @SerializedName("ref_name")
   private String refName = null;
@@ -213,22 +288,22 @@ public class Activity implements Serializable {
     this.isPrivate = isPrivate;
   }
 
-  public Activity opType(String opType) {
+  public Activity opType(OpTypeEnum opType) {
     this.opType = opType;
     return this;
   }
 
   /**
-   * Get opType
+   * the type of action
    *
    * @return opType
    */
-  @Schema(description = "")
-  public String getOpType() {
+  @Schema(description = "the type of action")
+  public OpTypeEnum getOpType() {
     return opType;
   }
 
-  public void setOpType(String opType) {
+  public void setOpType(OpTypeEnum opType) {
     this.opType = opType;
   }