It is to provide an improved method for preparation of microsphere from an emulsion wherein an organic phase containing an organic solvent having a boiling point lower than that of water and a hardly-water-soluble polymer is emulsified in an aqueous phase by an in-water drying method, which comprises: (1) using an apparatus equipped with a gas separation membrane; (2) supplying the emulsion to be subjected to in-water drying to one side of said gas separation membrane; (3) evaporating off the organic solvent contained in said emulsion to the other side of said gas separation membrane, which can remove the organic solvent with high efficiency and can be carried out in a closed system and hence is favorable from the environmental viewpoint.