Set Min width and max width for Button
<UserControl x:Class='SilverlightApplication3.MainPage' xmlns='http://schemas.microsoft.com/winfx/2006/xaml/presentation' xmlns:x='http://schemas.microsoft.com/winfx/2006/xaml' xmlns:d='http://schemas.microsoft.com/expression/blend/2008' xmlns:mc='http://schemas.openxmlformats.org/markup-compatibility/2006' mc:Ignorable='d' d:DesignWidth='640' d:DesignHeight='480'> <StackPanel Margin="3"> <TextBlock Margin="3" HorizontalAlignment="Center" Text="A Button Stack"></TextBlock> <Button Margin="3" MaxWidth="300" MinWidth="200" Content="Button 1"></Button> <Button Margin="3" MaxWidth="300" MinWidth="200" Content="Button 2"></Button> <Button Margin="3" MaxWidth="300" MinWidth="200" Content="Button 3"></Button> <Button Margin="3" MaxWidth="300" MinWidth="200" Content="Button 4"></Button> </StackPanel> </UserControl>