diff --git a/src/main/scala/app/CreateRepositoryServlet.scala b/src/main/scala/app/CreateRepositoryServlet.scala
index aff1e0c..f620ab3 100644
--- a/src/main/scala/app/CreateRepositoryServlet.scala
+++ b/src/main/scala/app/CreateRepositoryServlet.scala
@@ -10,8 +10,8 @@
 /**
  * Creates new repository.
  */
-class CreateRepositoryServlet extends ScalatraServlet with ServletBase {
-    
+class CreateRepositoryServlet extends ServletBase {
+  
   /**
    * Show the new repository form.
    */
@@ -23,42 +23,60 @@
    * Create new repository.
    */
   post("/") {
-    val repositoryName = params("name")
-    val description = params("description")
+    withValidation(validate, params){
+      val repositoryName = params("name")
+      val description = params("description")
     
-    val gitdir = getRepositoryDir(LoginUser, repositoryName)
-    val repository = new RepositoryBuilder().setGitDir(gitdir).setBare.build
+      val gitdir = getRepositoryDir(LoginUser, repositoryName)
+      val repository = new RepositoryBuilder().setGitDir(gitdir).setBare.build
     
-    repository.create
+      repository.create
     
-    val config = repository.getConfig
-    config.setBoolean("http", null, "receivepack", true)
-    config.save
+      val config = repository.getConfig
+      config.setBoolean("http", null, "receivepack", true)
+      config.save
     
-    val tmpdir = getInitRepositoryDir(LoginUser, repositoryName)
-    try {
-      // Clone the repository
-      Git.cloneRepository.setURI(gitdir.toURI.toString).setDirectory(tmpdir).call
+      val tmpdir = getInitRepositoryDir(LoginUser, repositoryName)
+      try {
+        // Clone the repository
+        Git.cloneRepository.setURI(gitdir.toURI.toString).setDirectory(tmpdir).call
     
-      // Create README.md
-      val readme = new File(tmpdir, "README.md")
+        // Create README.md
+        FileUtils.writeStringToFile(new File(tmpdir, "README.md"), if(description.nonEmpty){
+            repositoryName + "\n===============\n\n" + description
+          } else {
+            repositoryName + "\n===============\n"
+          }, "UTF-8")
     
-      FileUtils.writeStringToFile(readme, if(description.nonEmpty){
-          repositoryName + "\n===============\n\n" + description
-        } else {
-          repositoryName + "\n===============\n"
-        }, "UTF-8")
-    
-      val git = Git.open(tmpdir)
-      git.add.addFilepattern("README.md").call
-      git.commit.setMessage("Initial commit").call
-      git.push.call
+        val git = Git.open(tmpdir)
+        git.add.addFilepattern("README.md").call
+        git.commit.setMessage("Initial commit").call
+        git.push.call
       
-    } finally {
-      FileUtils.deleteDirectory(tmpdir)
+      } finally {
+        FileUtils.deleteDirectory(tmpdir)
+      }
+      
+      // redirect to the repository
+      redirect("/%s/%s".format(LoginUser, repositoryName))
     }
-      
-    // redirect to the repository
-    redirect("/%s/%s".format(LoginUser, repositoryName))
+  }
+  
+  get("/validate") {
+    contentType = "application/json"
+    validate(params).toJSON
+  }
+  
+  def validate(params: Map[String, String]): ValidationResult = {
+    val name = params("name")
+    if(name.isEmpty){
+      ValidationResult(false, Map("name" -> "Repository name is required."))
+    } else if(!name.matches("^[a-z0-6\\-_]+$")){
+      ValidationResult(false, Map("name" -> "Repository name contans invalid character."))
+    } else if(getRepositories(LoginUser).contains(name)){
+      ValidationResult(false, Map("name" -> "Repository already exists."))
+    } else {
+      ValidationResult(true, Map.empty)
+    }
   }
 }
\ No newline at end of file
diff --git a/src/main/scala/app/RepositoryViewerServlet.scala b/src/main/scala/app/RepositoryViewerServlet.scala
index f9b4c81..e878a30 100644
--- a/src/main/scala/app/RepositoryViewerServlet.scala
+++ b/src/main/scala/app/RepositoryViewerServlet.scala
@@ -18,7 +18,7 @@
 /**
  * The repository viewer.
  */
-class RepositoryViewerServlet extends ScalatraServlet with ServletBase {
+class RepositoryViewerServlet extends ServletBase {
   
   /**
    * Shows user information.
diff --git a/src/main/scala/app/ServletBase.scala b/src/main/scala/app/ServletBase.scala
index b0a88d9..8f5cd04 100644
--- a/src/main/scala/app/ServletBase.scala
+++ b/src/main/scala/app/ServletBase.scala
@@ -1,11 +1,36 @@
 package app
 
+import org.scalatra._
+import org.scalatra.json._
+import org.json4s._
+import org.json4s.jackson._
+
 /**
  * Provides generic features for ScalatraServlet implementations.
  */
-trait ServletBase {
+abstract class ServletBase extends ScalatraServlet with JacksonJsonSupport {
+  
+  implicit val jsonFormats = DefaultFormats
   
   // TODO get from session
   val LoginUser = System.getProperty("user.name")
+  
+  protected def withValidation(validator: Map[String, String] => ValidationResult, params: Map[String, String])(action: => Any): Any = {
+    validator(params).valid match {
+      case true  => action
+      case false => throw new RuntimeException("Invalid Request") // TODO show error page?
+    }
+  }
+  
+  case class ValidationResult(valid: Boolean, errors: Map[String, String]){
+    def toJSON(): JObject = {
+      JObject(
+        "valid"  -> JBool(valid),
+        "errors" -> JObject(errors.map { case (key, value) =>
+          JField(key, JString(value))
+        }.toList)
+      )
+    }
+  }
 
 }
\ No newline at end of file
diff --git a/src/main/twirl/main.scala.html b/src/main/twirl/main.scala.html
index 7c34ac7..3aa6f5e 100644
--- a/src/main/twirl/main.scala.html
+++ b/src/main/twirl/main.scala.html
@@ -13,6 +13,9 @@
       <script src="/assets/bootstrap/js/html5shiv.js"></script>
     <![endif]-->
     <link href="/assets/common/css/gitbucket.css" rel="stylesheet">
+    <script src="/assets/common/js/jquery-1.9.1.js"></script>
+    <script src="/assets/common/js/validation.js"></script>
+    <script src="/assets/bootstrap/js/bootstrap.js"></script>
   </head>
   <body>
     <div class="navbar navbar-inverse">
@@ -37,7 +40,5 @@
     <div class="container">
       @body
     </div>
-    <script src="/assets/common/js/jquery-1.9.1.js"></script>
-    <script src="/assets/bootstrap/js/bootstrap.js"></script>
   </body>
 </html>
\ No newline at end of file
diff --git a/src/main/twirl/newrepo.scala.html b/src/main/twirl/newrepo.scala.html
index 8d55193..737d118 100644
--- a/src/main/twirl/newrepo.scala.html
+++ b/src/main/twirl/newrepo.scala.html
@@ -1,9 +1,10 @@
 @()
 @main("Create a New Repository"){
-<form method="post" action="/new">
+<form id="form" method="post" action="/new" validate="true">
   <fieldset>
     <label for="name"><strong>Repository name</strong></label>
     <input type="text" name="name" id="name" />
+    <span id="error-name" class="error-message"></span>
   </fieldset>
   <fieldset>
     <label for="description"><strong>Description</strong> (optional)</label>
diff --git a/src/main/webapp/assets/common/css/gitbucket.css b/src/main/webapp/assets/common/css/gitbucket.css
index 38037bb..3d8e28b 100644
--- a/src/main/webapp/assets/common/css/gitbucket.css
+++ b/src/main/webapp/assets/common/css/gitbucket.css
@@ -11,6 +11,10 @@
   width: 920px;
 }
 
+span.error-message {
+  color: red;
+}
+
 .small {
   font-size: small;
 }
diff --git a/src/main/webapp/assets/common/js/validation.js b/src/main/webapp/assets/common/js/validation.js
new file mode 100644
index 0000000..330f22c
--- /dev/null
+++ b/src/main/webapp/assets/common/js/validation.js
@@ -0,0 +1,29 @@
+$(function(){
+	$.each($('form[validate=true]'), function(i, form){
+		$(form).submit(validate);
+	});
+});
+
+function validate(e){
+	var form = $(e.target);
+	
+	if(form.data('validated') == true){
+		return true;
+	}
+	
+	// TODO use $.post() instead of $.getJSON
+	$.getJSON(form.attr('action') + '/validate', $(e.target).serialize(), function(data){
+		// clear all error messages
+		$('.error-message').text('');
+		
+		if(data.valid){
+			form.data('validated', true);
+			form.submit();
+		} else {
+			$.each(data.errors, function(key, value){
+				$('#error-' + key).text(value);
+			});
+		}
+	});
+	return false;
+}