I am working in kuwait since 2001 , i am preparing file for canada , everything is ready but my police clearance certificate [ for kuwait ] was issued on june 7th 2003 , i am going to apply now , is it valid after one year ?

No, its not valid even Now. CIC always asks for latest PCC and as per CIC PCC validity is one year.

Cheers
Raj

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A person is never more on trial than in a moment of excessive good fortune.

Here is the text from CIC guide :

Police certificates and clearances:

You and your family members must provide us with a police certificate issued by the authorities of each
country in which you have lived for six (6) months or more since reaching the age of 18. Certificates must
be originals and issued within the last three months.
If you have been convicted of a criminal offence in Canada, your application cannot be approved unless you
receive a pardon. To avoid the unnecessary payment of processing fees for an immigration application that
will be refused, you should first apply for a pardon to the:

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A person is never more on trial than in a moment of excessive good fortune.