The effect of crude oil on some haematological parameters were studied in African catfish (Clarias gariepinus). A total of 30 catfish were grouped into 6 groups containing 5 catfish each. They were held for three (3) days in 5 different mixtures of crude oil polluted water (0.25%, 0.5%, 0.75%, 1%, and 1.5% v/v). Catfish in the control group were held in borehole water. At the expiration of 3 days, blood samples were collected and analysed. The red blood cell (RBC) count reduced with increasing concentration of crude oil, indicating an anaemic condition. This decrease also affected dependable factors such as packed cell volume (PCV), haemoglobin (Hb), mean corpuscular haemoglobin (MCH), and an increase in mean corpuscular haemoglobin concentration (MCHC). Furthermore, white blood cells (WBC) decreased, indicating susceptibility to stress and infection. Overall, the results indicated that exposure to crude oil has serious consequences on haematological parameters of catfish which may be attributed to the toxic components of crude oil. Keywords: Crude oil, Clarias gariepinus, RBC, PCV, Hb, MCH, MCHC, WBC