Provided is a safer, highly effective method for exterminating external parasites that parasitize the body surface of fish. A method for exterminating external parasites of marine fish using a low-concentration hydrogen peroxide solution, the method being characterized in that immersion is performed for 15 minutes or longer in a 30-150 ppm hydrogen peroxide solution. A method for exterminating external parasites of marine fish using a low-concentration hydrogen peroxide solution, the method being characterized in that the sides of the netting of a live-box are covered by a sheet to create a state in which seawater is retained inside, a hydrogen peroxide solution is introduced to make a calculated average concentration of 30-150 ppm in the seawater inside the live-box, and the sheet is removed after 15 minutes.
