A preparation method is reported for the microencapsulation of SiO2 by rapid expansion of supercritical solution with a nonsolvent. A suspension of SiO2 in carbon dioxide containing a cosolvent and dissolved polymer is sprayed through a nozzle to atmospheric pressure. After rapid expansion, polymer microspheres were obtained. The microspheres do not tend to agglomerate, since the pure cosolvent is a nonsolvent for the polymer. The structure and morphology of microspheres were investigated by SEM and TEM. The obtained polymer microspheres are microcapsules of SiO2 particles. The primary particle diameter and particle size distribution of microcapsules, could be controlled by changing the feed composition, pre-expansion pressure, temperature, and diameter of nozzle. The polymer feed composition is more effective than other factors on the control of particle size.