With D, L-lactic acid and N-epsilon-carbobenzoyloxy-L-lysine [Lys(Z)] as the starting monomer material and tin dichloride as the catalyst, the drug carrier material poly(lactic acid-co-N-epsilon-carbobenzoyloxy-L-lysine) was synthesized via direct melt polycondensation. The copolymer was systematically characterized with intrinsic viscosity testing, Fourier transform infrared spectroscopy, H-1-NMR, gel permeation chromatography, differential scanning calorimetry, and X-ray diffraction. The influences of different feed molar ratios were examined. With increasing molar feed content of Lys(Z), the intrinsic viscosity, weight-average molecular weight, and polydispersity index (weight-average molecular weight/number-average molecular weight) gradually decreased. Because of the introduction of Lys(Z) with a big aromatic ring into the copolymer, the glass-transition temperature gradually increased with increasing feed charge of Lys(Z), and all of the copolymers were amorphous. The copolymers, with weight-average molecular weights from 10,500 to 6900 Da, were obtained and could reach the molecular weight level of poly(lactic acid) modified by Lys(Z) via the ring-opening polymerization of the cyclic intermediates, such as lactide and morpholine-2,5-dione. However, a few terminal carboxyl groups might have been deprotected during the polymerization reaction under high temperatures. (c) 2011 Wiley Periodicals, Inc. J Appl Polym Sci 121: 420-426, 2011