Polymerization of styrene and methylmethacrylate was conducted in the presence of seeds and microwave irradiation. The particles were characterized by laser light scattering and transmission electron microscopy. Making comparison between two kinds of microsphere formation processes, we have obtained some information on the mechanism of the particle formation. For polystyrene the process was mainly conducted on the seeds. However, for polymethylmacrylate at the lower concentration range, the process was mainly conducted in the solution, in contrary, at higher concentration, it occured mainly on the seeds.
