Aliphatic polyesters such as polycaprolactone are now widely utilized as a green polymer to avoid serious environmental pollution due to diffusion of plastics waste. Such a polyester contains a carbonyl group in each repeating unit. The Norrish-type photo decomposition, therefore, is expected to occur in these polyester polymers. Accordingly, photo irradiation by a medium pressure mercury lamp was done to the polyester film. It was found that the aliphatic polyester could be utilized for a photodegradable plastics. Photodegradation behavior of the aliphatic polyesters was compared with the biodegradation behavior by means of electron microscopy.