Thanks for ur Reply...

i've already used it [:(] ... But its not working...

Here is My Code;

protected void cmbTradeType_SelectedIndexChanged(object sender, EventArgs e)

        {

            if(cmbTradeType.SelectedValue != "-1")

            {

                FillSettlementDate(cmbTradeType.SelectedValue, ""); //Function Called To Fill cmbSettlementDate

                cmbSettlementDate.Enabled = true;//Enable cmbSettlementDate

            }

            if (cmbTradeType.SelectedValue == "-1")

            {

                cmbSettlementDate.Enabled = false;

            }

Page.ClientScript.RegisterStartupScript(this.GetType(), "focus", "<SCRIPT language='javascript'> document.getElementById('ctl00_ContentPlaceHolder1_cfsTrade1_cmbSettlementDate').focus();</SCRIPT>", true); //Set Focus on cmbSettlementDate

        }

Now Control should be transferred to cmbSettlementDate, but its really not working [:'(]