A polystyrene (PSt)／nano-SiO2 nanocomposite was prepared through emulsion polymerization of styrene in the presence of SiO2

and the mechanism and process of the redispersion of the aggregated nano-SiO2 particles during emulsion polymerization were studied．It was found that the commercial nano-SiO2 particles were usually in the state of aggregation according to TEM and SEM results

and their diameter was over the range of nanometer. With the increase of the polymerization time

the conversion of styrene gradually increased and the latex diameter of the PSt／SiO2 microcapsule decreased．When the polymerization time reached 120 min

the conversion and the latex diameter tended to be constant．The TEM photograph also showed that the PSt／SiO2 microcapsule had the sea-island structure and the size of SiO2 particles was in the range of nanometer

which suggested that the aggregated nano-SiO2 particles were gradually redispersed during emulsion polymerization．FTIR studies approved that in addition to the formation of homopolymer the grafted polystyrene had also been produced on the SiO2 surface

which improved the interfacial compatibility between polystyrene and nano-SiO2．The released heat during the polymerization and the shear force were the main reasons causing the redispersion of the aggregated nano-SiO2．