Poly(e-caprolactone) (PCL) was prepared by ring- opening polymerization initiated with samarium acetate. The effects of reaction temperature, molar ratio of monomer/ initiator and reaction time on the conversion of e-CL to PCL and the molecular weight were investigated. The temperature was varied between 80 and 150 °C and the molar ratio of monomer to initiator between 107 and 1000 mol/mol. The results indicatethatthe samariumacetate (SmAc3) induces the polymerization of e-CL to high conversion and polyesters with number-average molecular weights of 3.43×10 3 to 12.60×10 3 were obtained. The polymers were characterized by Nuclear Magnetic Resonance ( 1 H-NMR), size exclusion chromatography (SEC). Based on the 1 H-NMR end-group analysis of low-molecular-weight PCL, it was proposed a coordination-insertion mechanism for the polymerization. Kinetics study indicated that the polymerization rate is first- order with respect to monomer concentration.