A biodegradable plastic composition which can be stably adjusted in biodegradation rate, and has greatly improved resistance to hydrolysis and weather, in particular the former, and durability resulting from the improved resistances; a molded article thereof; and a method for controlling biodegradation rate using the same composition. The biodegradable plastic composition comprising (A) 100 parts by weight of biodegradable plastic, (B) 0.01 to 10 parts by weight of a carbodiimide compound and (C) 0.01 to 10 parts by weight of at least one compound selected from the group consisting of benzotriazole-, triazine- and hydroxylamine-based compounds; the molded article thereof; and the method for controlling biodegradation rate using the same composition.