Monodispersed porous polystyrene beads crosslinked with divinylbenzene were prepared by in situ polymerization. For this objective, the preparation of uniform oil microdroplets in water was successfully achieved by using a Shirasu Porous Glass (SPG) membrane emulsifier (POEM (R) from Reika Kogyo Co, Ltd.), Separation abilities for a gel permeation chromatograph (GPC) column were discussed with polymer microbeads obtained by changing key experimental factors such as the pore sizes of the SPG membrane and diluents, Consequently, it was evident from gel permeation chromatography that the porous beads prepared by SPG emulsification can be used for the effective separation of a molecular weight range of 10(2) to 10(6).