Although u can set the maxbutton property to false at design time, this only works with NON-MDI forms....for your MDI forms u have to do it in code using windows API functions....i looked up several in the API text viewer & the code below will show how to disable the Maximize button on an MDI form & also how to prevent resizing:

Code:
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In the General declartions of a Module
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Private Declare Function SetWindowLong Lib "user32" Alias "SetWindowLongA" (ByVal hwnd As Long, ByVal nIndex As Long, ByVal dwNewLong As Long) As Long
Private Declare Function GetWindowLong Lib "user32" Alias "GetWindowLongA" (ByVal hwnd As Long, ByVal nIndex As Long) As Long

Private Const WS_THICKFRAME = &H40000
Private Const WS_MAXIMIZEBOX = &H10000
Private Const GWL_STYLE = (-16)


'This function will make sure the form that is passed to it
' thru its paramater has the Maximize button disabled & cannot
' be resized

Public Sub MaxBox(ByRef PsdForm As Form)
Dim lStyle As Long
lStyle = GetWindowLong(PsdForm.hwnd, GWL_STYLE)

lStyle = lStyle Xor WS_MAXIMIZEBOX Xor WS_THICKFRAME

Call SetWindowLong(PsdForm.hwnd, GWL_STYLE, lStyle)

End Sub

In the Load Event of the MDI form:
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Maxbox Me