The transparent poly(butyl acrylate-co-maleic anhydride)/silica [P(BA-co-MAn)/SiO2] has been successfully prepared from butyl acrylate-maleic anhydride copolymer P(BA-co-MAn) and tetraethoxysilane (TEOS) in the presence of 3-aminopropyltriethoxysilane (APTES) by an in situ sol-gel process. Triethoxysilyl group can be readily incorporated into P(BA-co-MAn) as pendant side chains by the aminolysis of maleic anhydride unit of copolymer with APTES, and then organic polymer/silica hybrid materials with covalent bonds between two phases can be formed via the hydrolytic polycondensation of triethoxysilyl group-functionalized polymer with TEOS. It was found that the amount of APTES could dramatically affect the gel time of sol-gel system, the sol fraction of resultant hybrid materials, and the thermal properties of hybrid materials obtained. The decomposition temperature of hybrid materials and the final residual weight of thermogravimetry of hybrid both increase with the increasing of APTES. Scanning electron microscopy (SEM) and atomic force microscopy (AFM) showed that the morphology of hybrid materials prepared in the presence of APTES was a co-continual phase structure.