Export DataTable to Excel File

use this code...

    dt = city.GetAllCity();//your datatable
    string attachment = "attachment; filename=city.xls";
    Response.ClearContent();
    Response.AddHeader("content-disposition", attachment);
    Response.ContentType = "application/vnd.ms-excel";
    string tab = "";
    foreach (DataColumn dc in dt.Columns)
    {
        Response.Write(tab + dc.ColumnName);
        tab = "\t";
    }
    Response.Write("\n");
    int i;
    foreach (DataRow dr in dt.Rows)
    {
        tab = "";
        for (i = 0; i < dt.Columns.Count; i++)
        {
            Response.Write(tab + dr[i].ToString());
            tab = "\t";
        }
        Response.Write("\n");
    }
    Response.End();

This snippet could be faster to implement:

// Example data
DataTable table = new DataTable();
table.Columns.AddRange(new[]{ new DataColumn("Key"), new DataColumn("Value") });
foreach (string name in Request.ServerVariables)
    table.Rows.Add(name, Request.ServerVariables[name]);

// This actually makes your HTML output to be downloaded as .xls file
Response.Clear();
Response.ClearContent();
Response.ContentType = "application/octet-stream";
Response.AddHeader("Content-Disposition", "attachment; filename=ExcelFile.xls");

// Create a dynamic control, populate and render it
GridView excel = new GridView();
excel.DataSource = table;
excel.DataBind();
excel.RenderControl(new HtmlTextWriter(Response.Output));

Response.Flush();
Response.End();