Enzyme-catalyzed ring-opening polymerization of a cyclic phosphate (ethylene isopropyl phosphate) was achieved in bulk by using porcine pancreas lipase (PPL) as a catalyst. It was found that the higher the polymerization temperature and lipase concentration, the faster is the polymerization rate. The yield is not very sensitive to the lipase concentration, while the molecular weight decreases with increasing lipase concentration. From C-13 and H-1 NMR analysis, the polymer has a phosphoric acid group at one end and a hydroxyl group at the other. The P-31{H-1} NMR spectrum indicated that some chain transfer might take place in the polymerization.