An experiment was conducted to study the effects of some selected pesticides on the mortality of tilapia fish (Oreochromis niloticus). We also observed water quality parameters of the experimental buckets. Six pesticides were used in this experiment. Among them three were insecticides (Malathion, Diaginon and Curatar) and three were herbicides (Amclore, Silah and Top). The pesticide Curatar had significant effect on the mortality of tilapia fish. Curatar proved to the most destructive effect on tilapia fish. It killed 1.859 out of six fingerlings. This was follwed by Diazinon, which killed 1.641 fishes. Again, Malathion followed Diazinon which also killed 1.391. After that, Silah was follwed by Malathion. Lastly Amclore (0.844) and Top (0.813) had identical toxicity in respect of killing fishes, and they killed the lowest number of fishes.