In advance of a discussion on structural effects on biodegradation, aliphatic polyesters as biodegradable structural materials were classified into four types regarding chemical structure, that is poly(-hydroxy acid), poly(โค-hydroxyalkanoate), poly(-hydroxyalkanoate) and poly(alkylene dicarboxylate), and reviewed on synthesis route, thermal and physical properties, and biodegradability. The biodegradation mechanism of these aliphatic polyesters were discussed on the major mode of hydrolysis reaction in regard whether it was enzyme-catalyzed or not, and the substrate specificities of enzymes, such as lipases or PHA depolymerases, were discussed on the hydrolysis of the aliphatic polyesters in respect of primary structure. Moreover, the biodegradation behaviors were exceedingly influenced by solid-state morphology in addition to primary structure. The rate of enzymatic degradation of polycaprolactone fibers drawn with various draw ratios was dependent on draw ratios, suggesting that crystallinity and orientation of them affected biodegradability by lipase. In the study of enzymatic degradation of films made from butylene succinate -ethylene succinate copolymer, the dependence of degradation rate on polymeric compositions was ascribed to the degree of crystallinity rather than the primary structure. These studies revealed that the degree of crystallinity was the major rate-determining factor of biodegradation of solid polymers.