Copolymer of L-lactide and epsilon-caprolactone [P(LLA-CL)] (50/50) was synthesized using stannous octoate and was stored at room temperature. The change in physical properties occurring during this storage at room temperature was investigated by differential scanning calorimetry (DSC), X-ray diffractometry, polarizing optical microscopy, tensile and bending tests, and light absorbance measurements. It was concluded that the increase in mechanical properties and light absorbance during storage can be ascribed to gradual selective crystallization of the L-lactide sequence in P(LLA-CL) at room temperature. (C) 2000 John Wiley & Sons, Inc.