Porcine pancreas lipase (PPL) immobilized on porous silica beads and employed successfully for ring-opening polymerization of ethylene isobutyl phosphate (EIBP) was investigated. The factors affecting the activity of the immobilized lipase were studied. A good coupling yield was achieved - 41.88 mg of native lipase/g of porous silica beads. We also studied the thermal properties of this immobilized lipase. The optimum temperature of this immobilized lipase was 70 degreesC. After incubation at 90 degreesC for 1 h, the activity of immobilized lipase remained above 70%. An enzyme-catalyzed ring-opening polymerization was achieved in bulk with Mn values ranging from 1642 to 5783 g/mol. It was found that recovered immobilized lipase was more active for the polymerization of EIBP than in the first use and Mn was significantly increased. The higher molecular weight can be gained with the propriety amount of immobilized lipase and a higher temperature.