The purpose of the present invention is to provide a method for suppressing infectious diseases of crustaceans for which there is no effective countermeasure, and which can cause total extermination once the disease occurs in a breeding ground. The method for suppressing infectious disease of crustaceans pertaining to the present invention is characterized by including a step for administering at least 0.001 g/kg body weight of Parachlorella algae per day to crustaceans.
