For the purpose of increasing the hydrophilicity of a polylactide, a new monomer, (3S)-3-[(benzyloxycarbonyl)methyl]morpholine-2,5-dione, was successfully polymerized. The benzyl protective group of the polymer was completely removed to give poly(glycolic acid-alt-L-aspartic acid). The structures and properties of both protected and deprotected polymers were carefully studied by NMR, GPC, and DCA. It is found that the morpholine-2,5-dione derivatives with side functional groups which have no substituent on the 6 position of the morpholine ring are much more reactive than those monomers with a substituent on the 6 position of the ring in polymerization. The resulting polymer shows promising hydrophilicity, as can be seen from the DCA result.