Enantioselective copolymerization of racemic substituted lactones with achiral lactones has been examined by using Candida antarctica lipase as catalyst. In the copolymerization of racemic beta -butyrolactone with 12-dodecanolide, the (S)-isomer was preferentially reacted to give the (S)-enriched optically active copolymer with enantiomeric excess of beta -butyrolactone unit = 69%, which is much larger than that of the homopolymerization under similar reaction conditions. The absolute configuration of P-butyrolactone unit in the copolymer was confirmed by the acid-catalyzed methanolysis to methyl S-hydroxybutyrate. delta -Caprolactone was also enantioselectively copolymerized by the lipase catalyst, to give the optically active polyester. The highest ee value (76%) was achieved by the copolymerization of delta -caprolactone and 12-dodecanolide in diisopropyl ether.