Fairly uniform microspheres of poly(styrene-co-methyl methacrylate) were prepared by employing a microporous glass membrane [Shirasu porous glass (SPG)]. The single-step SPG emulsification, the emulsion composed mainly of monomers, hydrophobic additives, and an oil-soluble initiator, suspended in the aqueous phase containing a stabilizer and inhibitor, was then transferred to a reactor, and subsequent suspension polymerization followed. The droplets obtained were polymerized at 75 degrees C under a nitrogen atmosphere for 24 h. The uniform poly(styrene-co-methyl methacrylate) microspheres with diameters ranging from 7 to 14 mu m and a narrow particle-size distribution with a coefficient of variation dose to 10% were prepared by using SPG membrane with a pore size of 1.42 mu m. The effects of the crosslinking agent and hydrophobic additives on the particle size, particle-size distribution, and morphologies were investigated. It was found that the particle size decreased with a narrower size distribution when the additives were changed from long-chain alkanes to long-chain alcohols and long-chain esters, respectively. Various microspheres with different morphologies were obtained, depending on the composition of the oil phase. The spherical poly(styrene-co-methyl methacrylate) particles without phase separation were obtained when using an adequate amount of the crosslinking agent and methyl palmitate as an additive.