Enzymatic synthesis of polyesters has been achieved in ionic liquids, 1-butyl-3-methylimidazolinium tetrafluoroborate (1) and butylmethylimidazolinium hexafluorophosphate (2). Candida antarctica lipase catalyzed the ring-opening polymerization of ε-caprolactone (3) or the polycondensation of diethyl esters (4) and glycols (5) in the ionic liquids. The polymerization of 3 proceeded efficiently in 1 to give the polymer with molecular weight of several thousands.