Abstract: The ring opening polymerization (ROP) of lactide in presence of amino acid was investigated. Effects of amino acid concentration, pH value, and reaction condition on the molecular weight of the polymer were discussed. For the ROP of D，L- lactide , the molecular weight of polymer increased with increasing basicity of amino acid. Under the condition of 150 °C for 48 h, when molar ratio of D，L-LA/L-lysine]=50/1, polymeric product with weight-average molecular weight of 12800 g/mol and polydispersity of / =2.11 was obtained. In the ROP of D, D- lactide and L, L- lactide, the racemization of the polymer increased with increasing basicity of amino acid.

Key words: natural amino acid, lactide, ring-opening polymerization, molecular weight, molecular weight distribution