To obtain a desired polymorphic composition of MPPO (4-(1-(2-(3-methoxyphenethyl)phenoxy)-3-(dimethylamino)propan-2-yloxy)-4 -oxobutanoic acid), operation conditions were sought for seeded and drowning-out batch crystallization. Polymorphic mixtures having the same composition with the seed were obtained by controlling the seeding temperature, because it determined the supersaturations for the crystallization of both polymorphs. Analyzing the changes in the solution concentration and monitoring the particle behavior with FBRM, different crystallization behaviors between the polymorphs were made clear.