Hi nedash,

Refer the below sample code without using any dll.

C#

protected void Page_Load(object sender, EventArgs e)
{
    DataTable dt = new DataTable();
    dt.Columns.AddRange(new DataColumn[3] { new DataColumn("Id", typeof(int)), new DataColumn("Name", typeof(string)), new DataColumn("Country", typeof(string)) });
    dt.Rows.Add(1, "John Hammond", "United States");
    dt.Rows.Add(2, "Mudassar Khan", "India");
    dt.Rows.Add(3, "Suzanne Mathews", "France");
    dt.Rows.Add(4, "Robert Schidner", "Russia");
    Response.ClearContent();
    Response.AddHeader("content-disposition", string.Format("attachment;filename={0}.xls", DateTime.Now.ToString("yyyy-MM-dd")));
    Response.ContentType = "application/vnd.ms-excel";
    string tab = "";
    foreach (DataColumn dataColumn in dt.Columns)
    {
        Response.Write(tab + dataColumn.ColumnName);
        tab = "\t";
    }
    Response.Write("\n");
    int i;
    foreach (DataRow dataRow in dt.Rows)
    {
        tab = "";
        for (i = 0; i < dt.Columns.Count; i++)
        {
            Response.Write(tab + dataRow[i].ToString());
            tab = "\t";
        }
        Response.Write("\n");
    }
    Response.End();
}

VB.Net

Protected Sub Page_Load(sender As Object, e As EventArgs) Handles Me.Load
    Dim dt As New DataTable()
    dt.Columns.AddRange(New DataColumn(2) {New DataColumn("Id", GetType(Integer)), New DataColumn("Name", GetType(String)), New DataColumn("Country", GetType(String))})
    dt.Rows.Add(1, "John Hammond", "United States")
    dt.Rows.Add(2, "Mudassar Khan", "India")
    dt.Rows.Add(3, "Suzanne Mathews", "France")
    dt.Rows.Add(4, "Robert Schidner", "Russia")
    Response.ClearContent()
    Response.AddHeader("content-disposition", String.Format("attachment;filename={0}.xls", DateTime.Now.ToString("yyyy-MM-dd")))
    Response.ContentType = "application/vnd.ms-excel"
    Dim tab As String = ""
    For Each dataColumn As DataColumn In dt.Columns
        Response.Write(tab + dataColumn.ColumnName)
        tab = vbTab
    Next
    Response.Write(vbLf)
    Dim i As Integer
    For Each dataRow As DataRow In dt.Rows
        tab = ""
        For i = 0 To dt.Columns.Count - 1
            Response.Write(tab & dataRow(i).ToString())
            tab = vbTab
        Next
        Response.Write(vbLf)
    Next
    Response.[End]()
End Sub

Below is another way.

C#

protected void Page_Load(object sender, EventArgs e)
{
    DataTable dt = new DataTable();
    dt.Columns.AddRange(new DataColumn[3] { new DataColumn("Id", typeof(int)), new DataColumn("Name", typeof(string)), new DataColumn("Country", typeof(string)) });
    dt.Rows.Add(1, "John Hammond", "United States");
    dt.Rows.Add(2, "Mudassar Khan", "India");
    dt.Rows.Add(3, "Suzanne Mathews", "France");
    dt.Rows.Add(4, "Robert Schidner", "Russia");
    DataTableToExcel(dt);
}

public void DataTableToExcel(DataTable dt)
{
    HttpResponse response = HttpContext.Current.Response;
    response.Clear();
    response.ClearHeaders();
    response.ClearContent();
    response.Charset = Encoding.UTF8.WebName;
    response.AddHeader("content-disposition", "attachment; filename=" + DateTime.Now.ToString("yyyy-MM-dd") + ".xls");
    response.AddHeader("Content-Type", "application/Excel");
    response.ContentType = "application/vnd.xlsx";
    using (StringWriter sw = new StringWriter())
    {
        using (HtmlTextWriter htw = new HtmlTextWriter(sw))
        {
            GridView gridView = new GridView();
            gridView.DataSource = dt;
            gridView.DataBind();
            gridView.RenderControl(htw);
            response.Write(sw.ToString());
            gridView.Dispose();
            dt.Dispose();
            response.End();
        }
    }
}

VB.Net

Protected Sub Page_Load(sender As Object, e As EventArgs) Handles Me.Load
    Dim dt As New DataTable()
    dt.Columns.AddRange(New DataColumn(2) {New DataColumn("Id", GetType(Integer)), New DataColumn("Name", GetType(String)), New DataColumn("Country", GetType(String))})
    dt.Rows.Add(1, "John Hammond", "United States")
    dt.Rows.Add(2, "Mudassar Khan", "India")
    dt.Rows.Add(3, "Suzanne Mathews", "France")
    dt.Rows.Add(4, "Robert Schidner", "Russia")
    DataTableToExcel(dt)
End Sub

Public Sub DataTableToExcel(dt As DataTable)
    Dim response As HttpResponse = HttpContext.Current.Response
    response.Clear()
    response.ClearHeaders()
    response.ClearContent()
    response.Charset = Encoding.UTF8.WebName
    response.AddHeader("content-disposition", "attachment; filename=" + DateTime.Now.ToString("yyyy-MM-dd") + ".xls")
    response.AddHeader("Content-Type", "application/Excel")
    response.ContentType = "application/vnd.xlsx"
    Using sw As New StringWriter()
        Using htw As New HtmlTextWriter(sw)
            Dim gridView As New GridView()
            gridView.DataSource = dt
            gridView.DataBind()
            gridView.RenderControl(htw)
            response.Write(sw.ToString())
            gridView.Dispose()
            dt.Dispose()
            response.[End]()
        End Using
    End Using
End Sub