Thanks for your help. I got the jquery autocomplete to work :-) The missing pieces I found at http://encosia.com/3-mistakes-to-avoi... 

After setting the contenttype on the request and packing the data in the correct way my webservice started returning json instead of XML.

 hi Tung i followed ur way like =

in page load code behind method i get the current url this way and assign to a control -

string current_page = Globals.NavigateURL(PortalSettings.ActiveTab.TabID,"", "mid" + ModuleId.ToString());
subCommentButton.Text = current_page;

also added method to call in code behind -

[WebMethod]
        public static string GetDate(int jewellerId, string locale)
        {
            //System.Threading.Thread.Sleep(2000);
            return jewellerId.ToString() + locale;

        }

then in view.ascx page i call the AjaxTest function on button click below -

function AjaxTest() {  

var test= $("#<%= subCommentButton.ClientID %>").val(); //getting the url
est);
        $.ajax({
            type: "POST",
            url: test+"/GetDate",
            data: '{ "jewellerId":"' + 123 + '", "locale":"c#" }',
            contentType: "application/json; charset=utf-8",
            dataType: "json",
            success: function (msg) {
                // Replace the div's content with the page method's return.
                $("#show").text(msg.d);
                msg.d);
            },
            error: function (XMLHttpRequest, textStatus, errorThrown) {
                extStatus);
            }
        });
}

But i get error alert !!! plz help what's wrong??