 <p>Try with this code:</p> <pre><code>var prm = Sys.WebForms.PageRequestManager.getInstance(); prm.add_beginRequest(BeginRequestHandler); function BeginRequestHandler(sender, args) { tinymce.execCommand('mceRemoveEditor', true, 'text_control_id'); } prm.add_pageLoaded(function (sender, e) { LoadTinyMCE(); }); </code></pre>