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,omega-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 13C 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.