Abstract: The sub-chronic and chronic exposure of Tilapia, Oreochromis niloticus to sublethal concentration of 5. 5 ppm cadmium (0. 3 of 96 h LC50) for 1, 3 and 5 weeks was studied. Exposure of Tilapia to cadmium resulted into a number of haematological alterations. Erythropenia, a marked decrease in values of haemoglobin content, haematocrit and mean corpuscular haemoglobin were observed at all experimental periods of cadmium exposure. The values of mean cell volume were decreased at the second and last periods. The levels of mean corpuscular haemoglobin concentration decreased significantly at first period compared to the control value.