Enzymatic ring-opening polymerization and copolymerization of a nine-membered lactone, 8-octanolide (8-OL), was performed in isooctane by using various lipases of different origin as catalyst. The polymerization behavior greatly depended on the lipase origin. Candida antarctica, and Pseudomonas cepacia. lipases (lipases CA and PC, respectively) showed high catalytic activity toward the present polymerization. Pseudomonas fluorescens lipase (lipase PF) also catalyzed the polymerization of 8-OL. The polymerization catalyzed by lipase CA proceeded much faster than that using other lipases. In the polymerization using lipase PC at 75 degrees C for 240 h, the polymer with number-average molecular weight of 1.6 x 10(4) was obtained. 8-OL monomer was recovered unchanged in the polymerization without the enzyme. The initial rate of the polymerization of lactones in different ring size was determined in the presence of 1-octanol. In case of lipase PC or PF, the rate increased with increasing ring size, whereas there was a minimum point for the rate in using 8-OL in the polymerization catalyzed by lipase CA. The enzymatic copolymerization of 8-OL with epsilon-caprolactone or 12-dodecanolide was performed to give the corresponding copolymers having molecular weights of several thousands. According to C-13 NMR analysis, the copolymer showed a random structure.