diff --git a/src/main/scala/app/CreateRepositoryController.scala b/src/main/scala/app/CreateRepositoryController.scala
index a9d2861..a622c88 100644
--- a/src/main/scala/app/CreateRepositoryController.scala
+++ b/src/main/scala/app/CreateRepositoryController.scala
@@ -22,7 +22,7 @@
   case class RepositoryCreationForm(owner: String, name: String, description: Option[String], isPrivate: Boolean, createReadme: Boolean)
 
   val form = mapping(
-    "owner"        -> trim(label("Owner"          , text(required, maxlength(40), identifier))), // TODO check existence.
+    "owner"        -> trim(label("Owner"          , text(required, maxlength(40), identifier, existsAccount))),
     "name"         -> trim(label("Repository name", text(required, maxlength(40), identifier, unique))),
     "description"  -> trim(label("Description"    , optional(text()))),
     "isPrivate"    -> trim(label("Repository Type", boolean())),
@@ -40,12 +40,20 @@
    * Create new repository.
    */
   post("/new", form)(usersOnly { form =>
+    val ownerAccount  = getAccountByUserName(form.owner).get
     val loginAccount  = context.loginAccount.get
     val loginUserName = loginAccount.userName
 
     // Insert to the database at first
     createRepository(form.name, form.owner, form.description, form.isPrivate)
 
+    // Add collaborators for group repository
+    if(ownerAccount.isGroupAccount){
+      getGroupMembers(form.owner).foreach { userName =>
+        addCollaborator(form.owner, form.name, userName)
+      }
+    }
+
     // Insert default labels
     createLabel(form.owner, form.name, "bug", "fc2929")
     createLabel(form.owner, form.name, "duplicate", "cccccc")
@@ -90,20 +98,26 @@
     createWikiRepository(loginAccount, form.owner, form.name)
 
     // Record activity
-    recordCreateRepositoryActivity(loginUserName, form.name, form.owner)
+    recordCreateRepositoryActivity(form.owner, form.name, loginUserName)
 
     // redirect to the repository
     redirect(s"/${form.owner}/${form.name}")
   })
+
+  private def existsAccount: Constraint = new Constraint(){
+    def validate(name: String, value: String): Option[String] =
+      if(getAccountByUserName(value).isEmpty) Some("User or group does not exist.") else None
+  }
+
   
   /**
    * Duplicate check for the repository name.
    */
   private def unique: Constraint = new Constraint(){
-    def validate(name: String, value: String): Option[String] = {
-      // TODO fix to retreive user name from request parameter
-      getRepositoryNamesOfUser(context.loginAccount.get.userName).find(_ == value).map(_ => "Repository already exists.")
-    }
+    def validate(name: String, value: String): Option[String] =
+      params.get("owner").flatMap { userName =>
+        getRepositoryNamesOfUser(userName).find(_ == value).map(_ => "Repository already exists.")
+      }
   }
   
 }
\ No newline at end of file
diff --git a/src/main/scala/app/RepositorySettingsController.scala b/src/main/scala/app/RepositorySettingsController.scala
index bfb7470..780a7f3 100644
--- a/src/main/scala/app/RepositorySettingsController.scala
+++ b/src/main/scala/app/RepositorySettingsController.scala
@@ -54,14 +54,19 @@
    * Display the Collaborators page.
    */
   get("/:owner/:repository/settings/collaborators")(ownerOnly { repository =>
-    settings.html.collaborators(getCollaborators(repository.owner, repository.name), repository)
+    settings.html.collaborators(
+      getCollaborators(repository.owner, repository.name),
+      getAccountByUserName(repository.owner).get.isGroupAccount,
+      repository)
   })
 
   /**
    * Add the collaborator.
    */
   post("/:owner/:repository/settings/collaborators/add", collaboratorForm)(ownerOnly { (form, repository) =>
-    addCollaborator(repository.owner, repository.name, form.userName)
+    if(!getAccountByUserName(repository.owner).get.isGroupAccount){
+      addCollaborator(repository.owner, repository.name, form.userName)
+    }
     redirect(s"/${repository.owner}/${repository.name}/settings/collaborators")
   })
 
@@ -69,7 +74,9 @@
    * Add the collaborator.
    */
   get("/:owner/:repository/settings/collaborators/remove")(ownerOnly { repository =>
-    removeCollaborator(repository.owner, repository.name, params("name"))
+    if(!getAccountByUserName(repository.owner).get.isGroupAccount){
+      removeCollaborator(repository.owner, repository.name, params("name"))
+    }
     redirect(s"/${repository.owner}/${repository.name}/settings/collaborators")
   })
 
diff --git a/src/main/scala/service/AccountService.scala b/src/main/scala/service/AccountService.scala
index 39ca18e..769f9b7 100644
--- a/src/main/scala/service/AccountService.scala
+++ b/src/main/scala/service/AccountService.scala
@@ -50,7 +50,7 @@
     Accounts insert Account(
       userName       = groupName,
       password       = "",
-      mailAddress    = "",
+      mailAddress    = groupName + "@devnull",
       isAdmin        = false,
       url            = None,
       registeredDate = currentDate,
diff --git a/src/main/twirl/settings/collaborators.scala.html b/src/main/twirl/settings/collaborators.scala.html
index 6131f7b..acd869b 100644
--- a/src/main/twirl/settings/collaborators.scala.html
+++ b/src/main/twirl/settings/collaborators.scala.html
@@ -1,4 +1,6 @@
-@(collaborators: List[String], repository: service.RepositoryService.RepositoryInfo)(implicit context: app.Context)
+@(collaborators: List[String],
+  isGroupRepository: Boolean,
+  repository: service.RepositoryService.RepositoryInfo)(implicit context: app.Context)
 @import context._
 @import view.helpers._
 @html.main("Settings", Some(repository)){
@@ -9,17 +11,21 @@
       @collaborators.map { collaboratorName =>
         <li>
           <a href="@url(collaboratorName)">@collaboratorName</a>
-          <a href="@url(repository)/settings/collaborators/remove?name=@collaboratorName" class="remove">(remove)</a>
+          @if(!isGroupRepository){
+            <a href="@url(repository)/settings/collaborators/remove?name=@collaboratorName" class="remove">(remove)</a>
+          }
         </li>
       }
     </ul>
-    <form method="POST" action="@url(repository)/settings/collaborators/add" validate="true">
-      <div>
-        <span class="error" id="error-userName"></span>
-      </div>
-      <input type="text" name="userName" id="userName" style="width: 300px; margin-bottom: 0px;"/>
-      <input type="submit" class="btn" value="Add"/>
-    </form>
+    @if(!isGroupRepository){
+      <form method="POST" action="@url(repository)/settings/collaborators/add" validate="true">
+        <div>
+          <span class="error" id="error-userName"></span>
+        </div>
+        <input type="text" name="userName" id="userName" style="width: 300px; margin-bottom: 0px;"/>
+        <input type="submit" class="btn" value="Add"/>
+      </form>
+    }
   }
 }
 <script>