Transparent polystyrene/silica nanocomposites were synthesized by casting the blend solutions of polystyrene (PS) derivatives and perhydropolysilazane (PHPS) and by calcinating the blend films of PS derivatives and PHPS at 100 degrees C for 3 h under steam. Poly (styrene-co-4-vinyl phenol)s [P(S-co-VPh)s], poly(styrene-co-hydroxymethyl styrene)s [P(S-co-HMS)s], poly(styrene-co-4-vinyl phenol)-block-PSs [P(S-co-VPh)-block-PSs], and poly(styrene-co-hydroxymethyl styrene)-block-PSs [P(S-co-HMS)-block-PSs] were used as the PS derivatives. The morphology of the microphase separation, transparency, the degree of grafting of PHPS onto PS derivatives, and surface hardness of the composites were investigated by transmission electron microscopy, UV-vis, FTIR, and nanoindentation, respectively. Degrees of grafting of PHPS onto PS derivatives and transparency of the composites of P(S-co-VPh)s and P(S-co-VPh)-block-PSs were higher than those of P(S-co-HMS)s and P(Sco-HMS)-block-PSs. Surface hardness of the composites of P(S-co-VPh)-block-PS was drastically increased from 0.22 to 0.55 GPa by increasing the weight fraction of silica to 33.7%. (C) 2005 Wiley Periodicals, Inc.