Set Stroke, StrokeThickness for Rectangle
<Window x:Class="WpfApplication1.Window1" xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation" xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml" Title="WPF" Height="350" Width="300"> <UniformGrid Columns="3" HorizontalAlignment="Center" VerticalAlignment="Center"> <Rectangle Stroke="Black" StrokeThickness="3" Height="60" Width="90" /> </UniformGrid> </Window>