How to apply textbox properties to autocompletebox in silverlight ?

It looks like the textbox is a private member of the control (at least the version I looked at). Depending on what you are trying to do, you can get the underlining textbox control by way of an event. For example, I wanted the text to be aligned left after the user moved off the control: private void txtAccount_LostFocus(object sender, RoutedEventArgs e) { TextBox textBox = (TextBox)e.OriginalSource; textBox.Select(0, 0); }