In this study, an oil separation device from the blow-by gas were designed to segregate the lubricant oil from the blow-by gas. The purified gas returns into the combustion chamber of IC engine through the intake manifold system to increase the fuel efficiency because the gas still has hydro-carbon fuel components with it. Two models of the blow-by gas separation system were developed. The Baffle-type separation system which incorporates the impinging method and Cyclone-type separation system that incorporates the gravitational method are those. From this numerical study, the simulation results showed that the Cyclone- type CCV(Crankcase Ventilation)System shows 2.1 times higher separation efficiency than that of the Baffle-type system. The pressure resistance of the CCV is about 4.8 times lower than that of the Baffle-type oil separator.