Different concentration of lead nitrate were exposed in Cyprinus carpio juveniles and adult fishes (0.0, 2.5, 5.0, 10 and 20 mg/l) and (0.0, 25, 50, 100 and 200 mg/l) respectively. Fishes were observed for any symptoms every 6 hr interval after exposure of lead nitrate until 5days. High dose exposed fish of both size showed high level of lead accumulated in their tissues. In juvenile fishes, 50% of fish death was observed in 10mg/l of lead nitrate exposed. And in adult fishes, 60% and 50% died after 96hr of exposure in 50mg/l and 100mg/l concentration respectively. However around 70mg/l of lead concentration may produce 50% of lethal rate in fish (LD50) after 96hr exposure. The effects of lead on fish observed during this experiment showed that caution should be exercised in allowing lead into the aquatic environment.