The enzymatic degradation and repolymerization were carried out with the objectives of developing the chemical recycling of aliphatic polyester-type plastics, such as the poly(butylene adipate) (PBA), poly(butylene succinate), and poly(butylene adipate-co-succinate) copolymers which are typical biodegradable plastics. They were degraded by lipase in an organic solvent solution containing a small amount of water to produce cyclic oligomers mainly consisting of the cyclic diester. The produced cyclic oligomer was readily repolymerized by lipase to produce a polyester having an equal or higher molecular weight compared to the parent polymer. As an example, PBA having an M-w of 22 000 was almost quantitatively transformed by lipase CA (Novozym 435) in water-containing toluene at 50 degreesC into the corresponding cyclic oligomers mainly consisting of dimers. Thus, the obtained oligomers were readily polymerized by lipase CA to produce the PBA with an M-w of 52 000.