The biodegradability of poly(delta-valerolactone-co-L-lactide)s was studied both with enzymatic (lipase from Rhizopus arrhizus) and nonenzymatic hydrolyses. The hydrolyzability was evaluated by recording the amount of the hydrolyzed water-soluble products. The enzymatic hydrolysis was considerably affected by copolymer composition. The copolyester, the most susceptible to enzymatic hydrolysis, was the one containing a 90 mol % delta-valerolactone unit. The copolymers were also nonenzymatically hydrolyzed at 70 degrees C. The results were similar to those of enzymatic hydrolysis, confirming the influence of copolymer composition on the hydrolyzability. However, the L-lactide rich copolymers were more susceptible to hydrolysis. These results suggest that poly(delta-valerolactone) is easily degraded by lipase, whereas poly(L-lactide) is degraded through simple hydrolysis.