Abstract: The soapless polystyrene (PSt) latex particles were prepared by using microwave irradiation in a closed reactor under controlled pressure, microwave irradiation and water bathing under normal pressure, respectively. The apparent molecular weight of the particles and their sizes and distribution were characterized by using static laser light scattering (SLLS) and dynamic laser light scattering (DLLS). It was found that microwave irradiation has important effect on the formation of the small size and monodisperse particles. The average numbers of the polymer chain in the PSt particles were calculated by the combination of gel permeation chromatography (GPC) and Zimm plot. The molecular weight of the PSt particles prepared by microwave irradiation under controlled pressure was bigger than that prepared by other ways. The results showed that the dispersity of the particles was not determined by the dispersity of the polymer chain directly. In the soapless emulsion polymerization under microwave irradiation, the latex particles composed of the intertwined polymer chain showed a od monodispersivity, although the polymer chains were not distributed uniformly .In studies of the aging of the homopolymerization and the copolymerization of emulsion, it was also found that the stability of the soapless polymer particles has an intimate relationship with the method of preparation, the structure and quality of the comonomer.