Beta-Propiolactone (BPL) was polymerized in bulk using lipase as a catalyst to form the polyester having a molecular weight of greater than 50000. The molecular weight of the polyesters produced by the lipase-catalyzed polymerization of BPL was inversely dependent on the concentration of lipase. Both molecular weight and polymerization speed were increased with increasing reaction temperature from 40 to 60 degrees C.