A new type of slow-release membrane-encapsulated urea fertilizer was prepared with starch-g-poly(vinyl acetate) (St-g-PVAc) as a biodegradable carrier material. By solution casting and washing rapidly with water the urea was individually encapsulated within the starch matrix modified by vinyl acetate through in situ graft-copolymerization. St-g-PVAc, which exhibits relatively low swellability, was synthesized by the reaction of starch and VAc in the presence of K2S2O8 as the initiator. The chemical structure of the St-g-PVAc and St-g-PVAc/urea composite film was confirmed by FTIR The release behavior of urea encapsulated in the films was studied. The experimental results indicated that the introduction of hydrophobic PVAc reduced the swellability of the starch matrix; the urea nitrogen slow-release time can reach 28 h in water. The St-g-PVAc/urea composite films could biodegrade in the soil environment.