<asp:UpdateProgress ID="UpdateProgress1" runat="server" AssociatedUpdatePanelID="UpdatePanel1">
<ProgressTemplate>
<div class="modal">
<div class="center">
<img alt="" src="loader.gif" />
</div>
</div>
</ProgressTemplate>
</asp:UpdateProgress>
<asp:UpdatePanel ID="UpdatePanel1" runat="server">
<ContentTemplate>
- PUT YOUR CONTENT HERE LIKE BUTTON , DROPDOWN ANYTHING THAT YOU WANT
</ContentTemplate>
</asp:UpdatePanel>