Silica sol was first used as an inorganic component to form poly(acrylamide) (PAM)/silica composite hydrogels via in situ free-radical polymerization. The gelation reaction of the composite materials was monitored on a rheometer, indicating that the gelling induction time becomes longer with the increasing content of silica sol. Compression strength and elastic modulus of the composite hydrogels were significantly improved by adding silica sol compared with pure PAM hydrogels. Silica particles formed by silica sol were dispersed on the surface of PAM polymer network in nanosize, promoting high degree of attachment to the polymer chain and enhancing the interfacial interaction between these two components. TGA analysis showed that the silica stiffens the hydrogel network by creating additional physical cross-linking point, but the breakable nature of the bonds and a broad distribution of distances between crosslinks may creates most likely a wide dissipative zone.