This article examines platform competition in mortgage backed security market. This market is two-sided in its nature. Mortgage backed securities are used to attract mortgage buyers on one side and property buyers on the other side. While government sponsored enterprises (e.g. Freddie Mac) can only securitize conforming mortgages, investment banks can securitize any type of mortgage. A game theoretic framework is employed to characterize possible equilibria with and without government regulation on investment banks behaviour. Empirical policy implications are also discussed.