The toxicity of both boron (H₃BO₃) and Cadmium (CdCl₂) was evaluated for Nile tilapia, Oreochromis niloticus. Six concentrations including control in Boron (H₃BO₃) experiment 0, 1, 20, 40, 80, 500 mg/l and five concentrations including control of Cadmium (CdCl₂) experiment 0, 15, 30, 60, 90 mg/l were used for evaluation of LC₅₀. Duplicate for each concentration was used and ten fish were used with an average weight of 50g ± 15 per aquaria. The 96 hours LC₅₀ was 290 mg/l for Boron. However, cadmium-treated groups showed no mortality. A histopathological examination of fish liver in Boric acid-treated groups showed moderate to significant changes including hydropic degeneration, congestion, dilated vessel, and focal necrotic changes. While the control group showed a healthy structure of the liver. In CdCl₂ treated groups, liver examination showed infiltration of inflammatory cells, congestion of blood vessels, and cytoplasm vacuolization.