Abstract: POSS/PS composite was synthesized through the condensation reaction of 3-chloropropylheptaisooctyl-POSS and functional PS. Sodium alkoxide group was attached to PS chain by three steps and the monofunctional POSS molecule containing one single 3-chloropropyl group was synthesized by the corner-capping method. The structures of all intermediates and the POSS/PS composite were well characterized by ¹H NMR，FTIR and XRD. The results show that the condensation reaction of 3-chloropropylheptaisooctyl-POSS and functional PS is efficient，and POSS is well dispersed in the composite. The thermal properties were investigated by a differential scanning calorimetry (DSC) and thermal gravimetric analysis (TGA). The data indicate that the glass transition temperature (T_g) and the initial decomposition temperature (T_dec) of POSS/PS composite are 16℃ and 69℃ higher than those of the pure PS，respectively，which is mainly due to the incorporation of POSS unit.