Enzymatic copolymerization of lactones, divinyl esters, and glycols has been performed using lipase as catalyst to produce ester copolymers. The monomers used in this study were 12-, 13-, and 16-membered lactones, divinyl esters of adipic and sebasic acids, and alpha ,w-glycols. Candida antarctica and Pseudomonas cepacia lipases showed relatively high catalytic activity for the present copolymerization, yielding the copolymer having relatively high molecular weight in moderate yields. From C-13 NMR analysis, the resulting product was not a mixture of homopolymers, but a copolymer derived from the monomers. NMR data and reaction monitoring results indicate that two different modes of polymerization, ring-opening polymerization and polycondensation, simultaneously take place through enzyme catalysis in one-pot to produce ester copolymers.