Chitosan-g-poly(vinyl alcohol) (PVA) copolymers with different grafting percent were prepared by grafting water-soluble PVA onto chitosan. The drug-release behavior was studied using the chitosan-g-PVA copolymer matrix containing prednisolone in a drug-delivery system under various conditions. The relationship between the amount of the released drug and the square root of time was linear. From this result, the drug-release behavior through the chitosan-g-PVA copolymer matrix is shown to be consistent with Higuchi＇s diffusion model. The drug-release apparent constant (K-H) was slightly decreased at pH 1.2, but increased at pH 7.4 and 10 according to the increasing PVA grafting percent. Also, K-H was decreased by heat treatment and crosslinking. The drug release behavior of the chitosan-g-PVA copolymer matrix was able to be controlled by the PVA grafting percent, heat treatment, or crosslinking and was also less affected by the pH values than was the chitosan matrix.