<telerik:RadGridView  Name="RadGridView1"
xmlns:telerik="http://schemas.telerik.com/2008/xaml/presentation"
AutoGenerateColumns="False"
ShowGroupPanel="False"
IsFilteringAllowed="False">
<telerik:RadGridView.Columns>
 <telerik:GridViewComboBoxColumn UniqueName="Status"
                                 HeaderText="STATUS">
 <telerik:GridViewColumn.CellTemplate>
   <DataTemplate>
      <ComboBox />
   </DataTemplate>
</telerik:GridViewColumn.CellTemplate>
</telerik:RadGridView.Columns>
</telerik:RadGridView>
 

private void FillStatusComboColumn()
{
var comboColumn = (Telerik.Windows.Controls.
GridViewComboBoxColumn)RadGridView1.Columns["Status"];
comboColumn.DataMemberBinding = new Binding("ActivityType");
comboColumn.ItemsSource = GetActivityTypes();
comboColumn.DisplayMemberPath =
"Name";
comboColumn.SelectedValueMemberPath =
"ID";
}

public class ActivityType
{
public string Name
{
get;
set;
}

public int ID
{
get;
set;
}

}

private System.Collections.IEnumerable GetActivityTypes()
{
List<ActivityType> ActivityTypes = new List<ActivityType>();

ActivityTypes.Add(new ActivityType() { ID = 0, Name = "" });
ActivityTypes.Add(new ActivityType() { ID = 1, Name = "Val1" });
ActivityTypes.Add(new ActivityType() { ID = 2, Name = "Val2" });
ActivityTypes.Add(new ActivityType() { ID = 3, Name = "Val3" });

return ActivityTypes;

}