Hi Singha Roy,
<pre lang="cs">Response.ClearContent();
Response.Buffer = true;
Response.AddHeader("content-disposition", string.Format("attachment; filename={0}", "Customers.xls"));
Response.ContentType = "application/ms-excel";
StringWriter sw = new StringWriter();
HtmlTextWriter htw = new HtmlTextWriter(sw);
gvdetails.AllowPaging = false;
gvdetails.DataBind();
gvdetails.RenderControl(htw);
Response.Write(sw.ToString());
Response.End();</pre>