<p>I am using an Infragistics UltraGrid in a WinForms application.<br>
Which event is raised on "check change" of checkbox in Infragistics UltraGrid?</p>

The AfterUpdate event of the checkbox is what you'll want to use.
If you're not able to trigger it, though, try adding this as well:
```
```
Private Sub YourGridcontrol_MouseDown(ByVal sender As Object, ByVal e As System.Windows.Forms.MouseEventArgs) Handles YourGridcontrol.MouseDown
    YourGridcontrol.PerformAction(Infragistics.Win.UltraWinGrid.UltraGridAction.EnterEditMode)
End Sub

Private Sub YourGridcontrol_MouseUp(ByVal sender As Object, ByVal e As System.Windows.Forms.MouseEventArgs) Handles YourGridcontrol.MouseUp
    YourGridcontrol.PerformAction(Infragistics.Win.UltraWinGrid.UltraGridAction.ExitEditMode)
End Sub
```
```
By default, just toggling the checkbox doesn't seem to trigger an Update. By making it enter/exit edit mode, the AfterUpdate should work as you want.
UPDATE: Or, like Vincent suggested, doing the PerformAction on the CellChange event should work, too.  The gist is the same.