private void ExportToExcel(DataGrid dgExport)
{
try
{
string strFileName = String.Empty, strFilePath= String.Empty;
strFilePath = Server.MapPath(@"../Excel/") + "ExcelFileName" + ".xls";
if (File.Exists(strFilePath))
{
File.Delete(strFilePath);
}
System.IO.StringWriter oStringWriter =new StringWriter();
System.Web.UI.HtmlTextWriter oHtmlTextWriter = new HtmlTextWriter(oStringWriter);
StreamWriter objStreamWriter;
string strStyle =@" .text { mso-number-format:\@; } 
";
objStreamWriter = File.AppendText(strFilePath);
dgExport.RenderControl(oHtmlTextWriter);
objStreamWriter.WriteLine(strStyle);
objStreamWriter.WriteLine(oStringWriter.ToString());
objStreamWriter.Close();
string strScript = "<script language=JavaScript>window.open('../Excel/" + "ExcelFileName" +
".xls','dn','width=1,height=1,toolbar=no,top=300,left=400,right=1, 
 
scrollbars=no,locaton=1,resizable=1');</script>";
if(!Page.IsStartupScriptRegistered("clientScript"))
{
Page.RegisterStartupScript("clientScript", strScript);
}
}
catch(Exception)
{
//Handle Exception
}
}

using System.Data.OleDb;
 
 
 
public partial class _Default : System.Web.UI.Page 
{
 
    protected void Page_Load(object sender, EventArgs e)
    {
        OleDbConnection ExcelConection = null;
        OleDbCommand ExcelCommand = null;
        OleDbDataReader ExcelReader = null;
        OleDbConnectionStringBuilder OleStringBuilder = null;
 
        try
        {
            OleStringBuilder =
                new OleDbConnectionStringBuilder(@"Provider=Microsoft.Jet.OLEDB.4.0;Data Source=C:\MyExcel.xls;Extended Properties='Excel 8.0;HDR=Yes;IMEX=1';");
            OleStringBuilder.DataSource = MapPath(@"~\MyExcel.xls");
 
            ExcelConection = new OleDbConnection();
            ExcelConection.ConnectionString = OleStringBuilder.ConnectionString;
 
            ExcelCommand = new OleDbCommand();
            ExcelCommand.Connection = ExcelConection;
            ExcelCommand.CommandText = "Select * From [Sheet1$]";
 
            ExcelConection.Open();
            ExcelReader = ExcelCommand.ExecuteReader();
 
            GridView1.DataSource = ExcelReader;
            GridView1.DataBind();
        }
        catch (Exception Args)
        {
            LabelErrorMsg.Text = "Could not open Excel file: " + Args.Message;
        }
        finally
        {
            if (ExcelCommand != null)
                ExcelCommand.Dispose();
            if (ExcelReader != null)
                ExcelReader.Dispose();
            if (ExcelConection != null)
                ExcelConection.Dispose();
        }  
    }
}