Spherical polymer particles with narrow size distribution have been prepared by aerosol-phase polymerization. The polyurea particles were prepared by the reaction of TDI(toluene-2,4-diisocyanate) or HDI(hexamethylene diisocyanate) droplets with EDA(ethylene diamine) vapor. The use of seed(NaCl) nuclei helped the polymer particles smaller in size and made the size distribution of the particles narrower. The particle size increased substantially with boiler temperature and decreased slightly with increasing the carrier gas flow rate. Increase in reboiler temperature improved the monodispersity of the particle size. Sphericity and surface smoothness of the particles were improved by decreasing particle size and controlling the reaction rates. The coating of TiO₂ on the surface of the prepared polymer particles was carried out by condensing Ti(Oet)₄ on the particle surface and subsequently reacting the liquid film with water vapor. The reaction system was also applied to prepare polyamide particles successfully.