The present study was conducted to determine the 96h-LC 50 of benomyl to the Nile tilapia, Oreochromis niloticus and to investigate the biochemical or hematological indices of blood and the alterations in the antioxidant enzymes of this fish in response to sublethal concentrations of benomyl. Fish weighing 71.61±12.05g were used in this study; they were subjected to fasting for 4 weeks before treatment. An aqueous solution of benomyl (0, 0.5, 1, 2, 4, 8, and 16mgL −1 ) was administered for 96h to determine the LC 50 . The 96h-LC 50 value of benomyl was 4.39 (3.23–5.60)mgL −1 in the present study. For 5 weeks, the aqueous solution of benomyl (0, 100, 200, and 400μgL −1 ) was administered to investigate its effect on the hematological parameters and antioxidant enzymes. The predominant hematological findings in fish exposed to benomyl were as follows: no significant change in the Hb (gdL −1 ) level, MCV (μm 3 ), MCH (pg) and MCHC (%) as compared to the control. Benomyl exposure led to greater increases in the GPT, GOT (Karmen-unit), LDH (Wroblewski unit), total cholesterol, Fe, and Ca (mgdL −1 ) values, whereas the levels of ALP (KA unit), total protein, triglyceride, albumin, and Mg (mgdL −1 ) did not increase. Benomyl increased the in vivo HSI (%), GST (nmolmin −1 mgprotein −1 ), and SOD (Umgprotein −1 ) values in the fish livers in the test group, unlike those in the control group for 5 weeks. At concentrations higher than 100μgL −1 , benomyl affected the GST and SOD levels of Nile tilapia in a dose- and time-dependent manner. The present findings suggest that the in vivo hepatotoxicity associated with benomyl may, in part, result from the hematological index, and antioxidants may provide limited protection against benomyl toxicity.