ABSTRACT-We examined the efficacy of febantel against the infection of the diclidophorid monogenean Heterobothrium okamotoi in cultured tiger puffer Takifugu rubripes. Febantel is a prodrug of fenbendazole, a benzimidazole drug, which is widely used in the field of veterinary medicine. Febantel was metabolized to fenbendazole in tiger puffer just like veterinary animals for oral administration. At the doses of 12.5 mg/kg and 25 mg/kg for 5 days, and 50 mg/kg for 3 days, 88%, 96% and 94%, respectively, of mature worms, and 97%, 95% and 97%, respectively, of immature worms were eradicated at 22-23∞C. These results suggest that febantel has high anti-H. okamotoi activity.