Please refer to the attached gif file. Workaround: close manually the drop down list when the auto-complete popup is shown: this.radDropDownList1.AutoCompleteMode = AutoCompleteMode.SuggestAppend; this.radDropDownList1.DropDownListElement.AutoCompleteSuggest.DropDownList.PopupOpened+=DropDownList_PopupOpened; private void DropDownList_PopupOpened(object sender, EventArgs e) { this.radDropDownList1.CloseDropDown(); }