don't i need a 4 yr degree for doing MBA from U.S.A??

Yes, you do for more than 90% of the universities. Apart from a 4 year degree, your require a minimum of 2 years work experience as well. Hope my answer has solved your query. If it has, kindly mark it as best answer.

3Yr Degree is enough

minimum qualification for any type of mba is that u should be a graduate