protected void btnExportToText_Click(object sender, EventArgs e)
{
        StringBuilder str = new StringBuilder();
        string strColumnName = string.Empty;

        foreach (DataColumn column in dt.Columns)
        {
            if (strColumnName != "")
            {
                strColumnName = strColumnName + "\t" + column.ColumnName.ToString();
            }
            else
            {
                strColumnName = column.ColumnName.ToString();
            }
        }

        str.Append(strColumnName);
        str.Append("\r\n");

        foreach (DataRow row in dt.Rows)
        {
            string strRow = string.Empty;
            // Loop through each column.
            foreach (DataColumn col in dt.Columns)
            {
                if (strRow != "")
                {
                    strRow = strRow + "\t" + row[col.ColumnName].ToString();
                }
                else
                {
                    strRow = row[col.ColumnName].ToString();
                }
            }
            str.Append(strRow);
            str.Append("\r\n");
        }

        Response.Clear();

        Response.AddHeader("content-disposition", "attachment;filename=ExportToText.txt");

        Response.Charset = "";

        Response.ContentType = "application/vnd.text";

        System.IO.StringWriter stringWrite = new System.IO.StringWriter();

        System.Web.UI.HtmlTextWriter htmlWrite = new HtmlTextWriter(stringWrite);

        Response.Write(str.ToString());

        stringWrite.Dispose();
        htmlWrite.Dispose();

        Response.End();
}

public override void VerifyRenderingInServerForm(Control control)
{
}

<%@ Page Language="C#" AutoEventWireup="true" EnableEventValidation="false" CodeFile="ExportToExcelWortText.aspx.cs" Inherits="ExportToExcelWortText" %>