<link href="//maxcdn.bootstrapcdn.com/bootstrap/3.3.0/css/bootstrap.min.css" rel="stylesheet" id="bootstrap-css"> <script src="//maxcdn.bootstrapcdn.com/bootstrap/3.3.0/js/bootstrap.min.js"></script> <script src="//cdnjs.cloudflare.com/ajax/libs/jquery/3.2.1/jquery.min.js"></script> <!------ Include the above in your HEAD tag ----------> <!-- Trigger the modal with a button --> <button type="button" class="btn btn-info btn-lg" data-toggle="modal" data-target="#myModal">Open Modal</button> <!--codigo ScriptManager.RegisterStartupScript(this, this.GetType(), "Pop", "openModal();", true); --> <script type="text/javascript"> function openModal() { $('#myModal').modal('show'); } </script> <!-- Modal --> <div id="myModal" class="modal fade" role="dialog"> <div class="modal-dialog"> <!-- Modal content--> <div class="modal-content"> <div class="modal-header"> <button type="button" class="close" data-dismiss="modal">×</button> <h4 class="modal-title">Modal Header</h4> </div> <div class="modal-body"> <p>Some text in the modal.</p> </div> <div class="modal-footer"> <button type="button" class="btn btn-default" data-dismiss="modal">Close</button> </div> </div> </div> </div>