A 24-week feeding experiment was conducted to assess whether males and females of Oreochromis niloticus exhibit differences in their hematological responses and organosomatic indices to dietary AFB1 contamination. Triplicate groups of O. niloticus (initial body weight: 24.1 ± 0.6 g) were fed with four diets (Diets 1 to 4) containing 0, 20, 200, and 2,000 μg AFB1 kg−1. A significant decrease (P<0.05) in hemoglobin (Hb), red blood cells (RBC), and hematocrit (Hct) was observed in AFB1 exposure groups, with the lowest levels recorded in the 2000 μg AFB1 kg−1 treatment. A significant increase in mean white blood cells (WBC), neutrophils, and lymphocytes was observed in AFB1 exposure groups. No sex-related differences in RBC, WBC, lymphocytes, monocytes, and neutrophils levels were observed. However, hemoglobin and hematocrit values for female O. niloticus were significantly lower than those for male O. niloticus. Organosomatic indices showed that the relative liver, kidney, and spleen weights were significantly higher (P<0.05) in the AFB1 supplemented group than in the control group. However, the effect of aflatoxin on organosomatic indices does not depend on sex but rather depends on the dose of aflatoxin in the diet. These results provide useful information for monitoring changes in the health status of male and female O. niloticus.