The effects of copper on gonadosomatic and hepatosomatic indices and on condition factor of Oreochromis niloticus were studied by exposing the animals to 0.1 mg/L Cu for 30 days. The mentioned indices and condition factor were calculated using standard formulas. No mortality was observed during the experiments. Copper increased the hepatosomatic index, but decreased both the gonadosomatic index and the condition factor. Variations in the measured parameters under the effect of copper were probably due to alteration of reproduction and growth, as a result of changes of the metabolic activities.