We have performed the ring-opening polymerization of lactones catalyzed by surfactant-coated lipases in organic solvents. A great improvement in the number-average molecular weight (M-n) of the produced polymer was observed compared to that of the lyophilized native lipase. The M-n vs monomer conversion profile suggests that the polymerization catalyzed by the surfactant-coated lipase is a step polymerization, whereas that catalyzed by lyophilized lipase powder is a chain polymerization. The effects of reaction temperature and the reaction solvent on the polymerization of lactones were also investigated.