In vitro synthesis of aliphatic polyesters was achieved by lipase-catalysed polymerization. A lipase-catalysed polycondensation of a dicar☐ylic acid and a glycol proceeded in an aqueous medium in which a dehydration took place in water. From a combination of sebacic acid and 1,8-octanediol, the corresponding polyester with a molecular weight of 1600 was obtained. Lipase also catalysed a ring-opening polymerization of lactones with different ring sizes. The polymerization behaviors depended on the lipase origin and the monomer structure. Macrolides (12-, 13- and 16-membered) showing much lower anionic polymerizability were enzymatically polymerized faster than ɛ-caprolactone. The lipase-catalysed polymerizability of these lactones was evaluated by Michaelis-Menten kinetics. The enzymatic ring-opening polymerization of lactones was expanded to an enantioselective polymerization of 3-methyl-4-oxa-6-hexanolide. The polymerization of the ( S)-isomer proceeded much faster than that of the ( R)-isomer. Single-step synthesis of end-functional polymers, methacryl-type macromonomer and a telechelic polyester having a car☐ylic acid group at both ends, was achieved by the polymerization in the presence of vinyl methacrylate and divinyl sebacate, respectively. Lipase catalysis provided the copolymerization of lactones, dicar☐ylic acid divinyl esters and glycols, in which two different types of polymerization—ring-opening polymerization and polycondensation—simultaneously occurred via the same acyl-lipase intermediate.