Abstract: In order to evaluate the reasonable dosage and safety of copper (II) sulfate, metrifonate and povidone-iodine, which are commonly used in aquaculture, and their toxic effects on GIFT tilapia (Oreochromis niloticus), we tested their acute toxicity and histopathological effects on GIFT tilapia under hydrostatic conditions. The results show that the LC₅₀s (24, 48 and 96 h) of copper sulfate were 13.715, 10.351 and 5.896 mg∙L⁻¹, respectively, and the safety concentration was 1.769 mg∙L⁻¹. The LC₅₀s (24, 48 and 96 h) of trichlorfon were 43.036, 25.887 and 16.689 mg∙L⁻¹, respectively, and the safety concentration was 2.810 mg∙L⁻¹. The LC₅₀s (24, 48 and 96 h) of povidone iodine were 10.509, 9.301 and 8.674 mg∙L⁻¹, respectively, and the safety concentration was 2.190 mg∙L⁻¹. Histopathological observation suggests that copper sulfate exposure can cause blurred gill filament outline, vacuolation of gill tissue, enlargement of liver tissue gap, vacuolation and nuclear atrophy, damage of nerve fibers in brain tissue, cell apoptosis, damage of renal tubular structure and nuclear membrane. Trichlorfon exposure can cause gill tissue damage and cell apoptosis, liver tissue denuclearization, mitochondrial swelling and vacuolation, brain tissue nerve fiber damage, nuclear pyknosis and renal interstitial hemorrhage. Exposure to povidone iodine can cause atrophy of gill filaments, incomplete structure of mitochondrial bilayer membrane, vacuolation of liver tissue, apoptosis of cells, and slight damage of nerve fibers. In conclusion, copper sulfate, trichlorfon and povidone iodine are relatively safe drugs for tilapia, but their dosage should be carefully controlled to avoid irreversible tissue damage.