One way:
Sub addFolder()
Dim pth As String
pth = "I:\Mybackup\"
If Dir(pth, vbDirectory) = "" Then
MkDir pth
Else
MsgBox "exists"
End If
End Sub

Another way:
On Error Resume Next
MkDir "I:\Mybackup\"
On Error GoTo0

I personally prefer the first way.
dan wrote:
Sub test()
' I want to creat a folder if that folder doesn't exist in the path.
' The following statement is not supported. What is the right way?, Please.

If Not Application.exist("I:\Mybackup\") Then MkDir ("I:\Mybackup\")
End Sub