PS/CNTs were prepared by a simple suspension polymerization method. TEM images showed that CNTs are wrapped in PS particles which are larger than pure PS particles, and it can be proved by DLS tests. TGA showed that the temperature of maximum speed on loss in weight of PS in composites is 80 ℃ higher than that of pure PS. And GPC tests also showed that the molecular weight of PS in composites is much higher than that of pure PS. So the CNTs have joined the polymerization of PS and bonded with PS which lead to an increase in polymerization extent of PS.