Abstract: PMMA/SiO₂ nanocomposites were prepared in the presence of a silane coupler(WD-20) by the in situ sol-gel process. Furthermore, the effect of coupler content on the morphology and properties of the PMMA/SiO₂ nanocomposites material was investigated by using UV-vis spectroscopy,FT-IR, SEM and heat distortion analysis.The results showed that, with WD-20 content increasing, the transmittance and glass transition temperature of the nanocomposites increased while the sol-fraction and the size of dispersed SiO2 phase in nanocomposites decreased.While the molar ratio of WD-20 and tetraethyl orthosilicate(TEOS) was 0.2, the sol-fraction of the prepared nanocomposites was 6%,glass transition temperature was above 250 ℃ and the transmittance was more than 80% at the wavelength between 450 nm and 800 nm and the size of dispersed SiO₂ phase was less than 100 nm.