The definition of biodegradable plastics, it is to point to in nature, such as soil, sand, water environment, water environment, certain conditions such as composting and anaerobic digestion conditions, the degradation caused by microbial action of the existence of nature, and eventually decomposed into carbon dioxide (CO2) and/or methane (CH4), water (H2O) and mineralization of the containing element inorganic salt, and the new biomass (such as the body of microorganisms, etc.) of plastic.