<select runat="server" id="sctFieldMain">
                 <option></option>
                   </select>

Script

   $(xml).find("FieldMain").each(function()
 { 
    var value=$(this).find('Title').text()
     $('#<%=sctFieldMain.ClientID %>').
      append($("<option></option>").
      attr("value",value).
      text(value)); 
  });

 alert($("#<%=sctFieldMain.ClientID %> option:selected").text());

this retrun <%=sctFieldMain.ClientID %>

or

alert($("#<%=sctFieldMain.ClientID %> option:selected").val());

this retrun undefined

or

alert($("#<%=sctFieldMain.ClientID %> option:selected").html());

return null

i like get Cureent Text. that selected