Abstract: The present invention aims to provide a method of producing methionine by hydrolyzing M-hydantoin in the presence of a basic potassium compound, which can effectively prevent corrosion of reaction vessels in both the liquid phase and gaseous phase of a hydrolysis solution even at a higher temperature, and enables a longer period of stable production of methionine. Provided is a method of producing methionine, comprising hydrolyzing 5-(?-methylmercaptoethyl)hydantoin in water in the presence of a basic potassium compound in a reaction system having a potassium concentration of not more than 9 wt % at a temperature of not less than 170° C.