Optically pure esomeprazole and its salt can be simply prepared by dissolving (S)-(−)-binol, a weak base and the racemic form of omeprazole in a mixture of a water-compatible organic solvent and water at a high temperature, cooling the mixed solution to crystallize the inclusion complex of esomeprazole and (S)-(−)-binol, and removing the (S)-(−)-binol moiety from the crystallized inclusion complex.