Hi Parastoo ,
Welcome to this Microsoft Project newsgroup
There are three palces where you can change the date format and when you go
between software programs they must be the same. So:
1. Control Panel - find the Regional and Language Options, which is
probably set up for your country and note the Date format set up for your
computer.
2. Excel - select all the columns containing dates and go to
Format/Cells/Date and select the same format.
3. Project - Tools/Options.../ View tab and select the same Date format.
However, it is possible that the date format for your country is not
available in Project. If this is so, then you will have to accept an
alternative in Project and then reset Excel to match. If that still doesn't
work, you may have to select a different setting for your Region.
FAQs, companion products and other useful Project information can be seen at
this web address: <
http://www.mvps.org/project/>
Hope this helps - please let us know how you get on

)
Mike Glen
MS Project MVP