Thanks. I found the difference using IsEmpty Function.
Sub test()
Dim MyVar, MyCheck
MyCheck = IsEmpty(MyVar) ' Return True
MyVar = Cells(1, 1) ' Cells(1, 1) = ""
MyCheck = IsEmpty(MyVar) ' Return False
Cells(1, 2).ClearContents
MyVar = Cells(1, 2)
MyCheck = IsEmpty(MyVar) ' Return True
End Sub