O-Methacryloyl-N-(tent-butoxycarbonyl)-beta-hydroxyaspartic acid dimethyl ester was synthesized by methyl esterification of beta-hydroxyaspartic acid, followed by protection of the amino group with the tert-butoxycarbonyl group and then the reaction of the hydroxyl group with methacryloyl chloride. The monomer efficiently underwent radical polymerization to afford the corresponding polymer with a number-average molecular weight of 42,000 in good yields. The alkaline hydrolysis of the polymer occurred not only at the methyl ester but also at the ester moiety between the main and side chains of the polymer. The methyl ester-free polymer gradually released beta-hydroxyaspartic acid moiety in a phosphate buffer solution with pH = 7.3 and 7.8.