hi Anandm

still not works....

here's my code for bind dropdownlist from database with field "nik"

and code form bind dropdown list to gridview

code bind dropdown list fromdatabase---

Private Sub ddlnik_Load(sender As Object, e As EventArgs) Handles ddlnik.Load
        Call konek_sql_server()
        cmd_sql_server = New SqlCommand("select nik from siswa", conn_sql_server)
        dr_sql_server = cmd_sql_server.ExecuteReader
        ddlnik.Items.Clear()
        While dr_sql_server.Read
            ddlnik.Items.Add(dr_sql_server("nik").ToString())
        End While
        dr_sql_server.Close()
            ddlnik.Items.Insert(0, New ListItem("Nik", "Nik or your value"))
    End Sub

code bind dropdown to gridview---

Protected Sub ddlnik_SelectedIndexChanged(sender As Object, e As EventArgs) Handles ddlnik.SelectedIndexChanged
        Call konek_sql_server()
        ds_sql_server = New DataSet()
        cmd_sql_server = New SqlCommand("select siswa.nik,siswa.nama,siswa.fakultas,siswa.jurusan,nilai.nilai1,nilai.nilai2,nilai.nilai3 from siswa inner join nilai on nilai.nik =siswa.nik where siswa.nik like @nik + '%'", conn_sql_server)
        cmd_sql_server.Parameters.AddWithValue("@nik", ddlnik.SelectedItem.Value)
        da_sql_server = New SqlDataAdapter(cmd_sql_server)
        da_sql_server.Fill(ds_sql_server)
        gv_siswa.DataSource = ds_sql_server
        gv_siswa.DataBind()
    End Sub

Hi Ruben12345,

You are binding the dropdownlist in wrong way refer below articles then you will have idea where you are going wrong

Bind (Populate) ASP.Net DropDownList using DataReader in C# and VB.Net

Bind / Fill / Populate DropDownList control from database in ASP.Net using C# and VB.Net

Dear AnandM

Well Done..It works i think i missed "If Not Me.IsPostBack"

Thanks For Your Help

Cheerss