Korea relies more than 70 percent of food supply on a limited number of exporting counties. If the suppliers possess market power, the food security matters. This study tested whether the major exporting countries of corn and wheat have power of determining market prices and enjoy oligopolistic profit in Korea. The empirical results indicate that Korea shows a high degree of import loyalty toward U.S. products. It is evident that the U.S. and Australia have market power in the wheat market, while no distinct power is detected in the corn market. The result for the corn market seems to reflect the severe price competition between the two major exporters, the U.S. and China. It is also shown that the launch of the WTO does not significantly change the structure of market power in the markets considered.