Polymeric divinylbenzene microspheres (MS) of narrow size distributions were prepared by microchannel (MC) emulsification and subsequent polymerization. Using two types of MC plates, large MS with 9.2 mum diameter on average and 5.7% coefficient of variation, as well as small MS with 3.4 mum diameter on average and 7.4% coefficient of variation were prepared. The MS diameter can be controlled by the size of the MC. This method is advantageous for synthesizing polymeric MS of narrow size distributions because of its simplicity.