Ring-opening polymerization of six lactones and condensation polymerization of six linear hydroxyesters were carried out at 45 degrees C using a lipase from Pseudomonas sp. Ring-opening polymerization of the lactones gave both higher molecular weight and higher monomer conversion than condensation of corresponding linear hydroxyesters. Lipase-catalyzed copolymerization of epsilon-caprolactone with lactide and cyclopentadecanolide gave higher molecular weight compared with copolymerization of epsilon-caprolactone with corresponding linear hydroxyesters.