or
var reportProcessor = new Telerik.Reporting.Processing.ReportProcessor(); Telerik.Reporting.Processing.RenderingResult result = reportProcessor.RenderReport("xlsx", reportToExport, null); string fileName = reportName + ".xlsx"; Response.Clear(); Response.Charset = ""; Response.ContentType = "application/vnd.xlsx"; Response.Cache.SetCacheability(HttpCacheability.Private); Response.Expires = -1; Response.Buffer = false; Response.AddHeader("Content-Disposition",string.Format("{0};FileName=\"{1}\"", "attachment", fileName)); Response.OutputStream.Write(result.DocumentBytes, 0, result.DocumentBytes.Length); Response.End();