This study aimed to evaluate the effectiveness of closed season policy using an integer linear programming, targeting the large purse seine fishery in Korea. In the analysis, based on Cheng and Townsend(1993), fishing effort (fishing days by month) was assumed to be distributed for profit maximization of vessels and catch of immature fish was estimated. The analytical results showed that the effects of closed season policy would vary in accordance with the monthly closures in terms of fishing profits and catch of immature fish. A closed season policy by month had different effects on fishing profits and catch of immature fish by species. It implies the importance of considering seasonal changes of fish species when limiting fishing efforts with the closed season policy.