I am a United State citizen and bringing my parents in 2-3 months on tourist visa from India. Can I claim them as my dependents for my tax purpose.

Yes, if they complete substantial presence test in the year, and you provide more than half of their support for the year and your parent's worldwide income is not more than $3,650 (for 2009). Your U.S. Tax Return: Substantial Presence Test (http://taxipay.blogspot.com/2008/04/substantial-presence-test.html)