100 mu m porous p(styrene-co-divinylbenzene)(PS-DVB) microspheres were synthesized by employing a particular membrane emulsification technique, and subsequent swelling of the seed droplets. DVB dissolving a water-insoluble substance, hexadecane (HD), and an initiator was permeated through a SPG (Shirasu porous glass) membrane, and the uniform (seed) droplets were released to a stabilizer solution acting as the continuous phase. The average droplet size was around 30 mu m, and this emulsion was mixed with a secondary emulsion of much smaller size consisting of more hydrophilic components, a mixture of styrene, middle chain alcohol (C6 to C8), dichlorobenzene, and isoamyl acetate, which promotes the degradative diffusion process of the components. After all the droplets in the secondary emulsion virtually disappeared, the seed droplets were swollen to a maximum 110 mu m. Polymerization was carried out at 348 K under a nitrogen atmosphere. Uniform porous spheres of 100 mu m with the coefficient of variation less than 10% were obtained. Specific surface area was 350 m(2)/g. Careful controlling of the specific gravity of swollen droplets and the choice of solvents balancing between the good solvency for the polymer and polarity (solubility in water) proved vital in order that the polymerization may proceed without an extensive phase separation in the early stage, which eventually induces breakup of the droplets. The three component system, isoamyl acetate-hexanol-o-dichlorobenzene, provided an adequate cosolvent for these purposes.