Abstract: A 84-day feeding trial was conducted to evaluate the effects of dietary aflatoxin B₁ (AFB₁) on growth, physiological responses, histological changes, and accumulation in juvenile grass carp (Ctenopharyngodon idellus). Triplicate groups of grass carp (2.90±0.16) g were fed with six semipurified diets formulated with isonitrogenous (crude protein: 32.96%), isocaloric (gross energy: 14.55 kJ/g) containing 0, 10, 20, 100, 1000 and 5000 μg/kg AFB₁. AFB₁ did not significantly impact behavior, the survival rate, final body weight (FBW), feeding rate (FR), specific growth rate (SGR) or feed efficiency (FE). No significant differences were found in hepatosomatic index (HSI) and viscera index (VSI) among all groups. AFB₁ had no significant effect in activities of serum alanine aminotransferase (ALT), aspartate aminotransferase (AST), alkaline phosphatase (ALP), superoxide dismutase (SOD) and glutathione peroxidase (GSH-Px). No significant histological lesions in hepatopancreas and kidney were identified between the control and increasing AFB₁ treatments. No AFB₁ residue was detected in muscles when fish fed with AFB₁ up to 1000 μg/kg, however, tiny dose (1.21±0.18) μg/kg of AFB₁ were detected in muscles in the group with 5000 μg/kg AFB₁, which was below the safety limitation of FDA. The results indicated that juvenile grass carp is a little susceptible species to AFB₁ exposure up to approximately 5000 μg/kg diet (determined level was 4979.2 μg/kg diet), at least for 84 days.