A nanocomposite hydrogel of poly(vinyl alcohol) (PVA) and polystyrene (PS)-poly(N-vinylacetamide) (PNVA) colloid particles was prepared by repeated freezing and thawing. The polymer colloid was synthesized by soap-free emulsion polymerization, and its molecular weight was controlled by varying the initiator concentration. The biologically safe PNVA hydrogen-bonds with PVA to form a network. To prepare a hydrogel with higher mechanical strength, a composite of PVA with uniformly dispersed PS-PNVA particles was prepared. This gel was evaluated in terms of the swelling characteristics and mechanical properties, for its application to biomaterials.