Biodegradable polymers poly(D,L-lactide) PDLLA was synthesized by a ring-opening polymerization process of ox-lactide. Maghnite-H+. (Mag-H+.), a montmorillonite sheet silicate clay exchanged with protons, was used as a non-toxic catalyst to induce the polymerization. Various techniques, including H-1 NMR, IR, DSC, GPC and viscosimetry, were used to elucidate structure and thermal properties of resulting polymer. Effect of Mag-H+/D,L-lactide weight ratio, temperature, solvent, and time reaction on the rate of polymerization and on average molecular weight of the resulting polymer, was studied. The polymerization rate increases with increasing of temperature and proportion of catalyst. A cationic mechanism was proposed. Mechanism studies showed that monomer inserted into the growing chains with the acyl-oxygen bond scission rather than the break of alkyl-oxygen bond. (C) 2010 Elsevier Ltd. All rights reserved.