Micron-sized, cross-linked polystyrene (PS) particles with different morphologies were prepared by the developed dispersion polymerization. By scanning electron microscope (SEM) observation, it was found that these PS particles had interesting shapes such as deformed sphere, hollow hemisphere and spheroid-like shape when initial monomer concentration, reaction time, and temperature and addition way of the reagent added in the third stage were different. The shape of the PS particles was changed from hollow hemisphere to spheroid-like shape with prolongation of the reaction time. It was remarkable that the rough surface of hollow-hemisphere-like PS particles became smooth and the hollow structure of smooth-hollow-hemisphere-like PS particles grew into solid structure at the same time. The formation mechanism behind these phenomena was discussed. POLYM. ENG. SCI., 51: 1170-1177, 2011. (C) 2011 Society of Plastics Engineers