Methionine is produced in an improved yield while reducing the load of waste water disposal by a process including the steps of:(A) adding at least one compound selected from potassium carbonate, potassium bicarbonate and potassium hydroxide to a solution containing 5-(.beta.-methylmercaptoethyl)hydantoin, (B) saturating the resulting solution with carbon dioxide gas and separating deposited methionine while leaving a first filtrate behind,(C) transferring part or whole of the first filtrate to step (D),(D) heating the transferred filtrate, adding a water-miscible solvent to it and saturating it with carbon dioxide gas to deposit methionine and potassium bicarbonate, and separating these deposits while leaving a second filtrate behind, and(E) returning the second filtrate to step (A) if desired.