Use Line break to add new line to TextBlock
<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'> <Grid x:Name="LayoutRoot" Background="White"> <StackPanel Orientation="Vertical" Background="Yellow"> <TextBlock Width="400" Text="My first text" FontSize="32"> <LineBreak/> <Run FontFamily="Webdings">this is a test</Run> <LineBreak/> <Run>asd</Run> <LineBreak/> <Run>asdf</Run> </TextBlock> </StackPanel> </Grid> </UserControl>