A 96-h copper acute toxicity for rainbow trout was investigated through static method. The toxicity test was conducted at a pH of 7.4 and temperature of 15 ÚC. Concentrations of copper ranged from 0.0 to 1.5 mg/L. The concentrations of copper that killed 50%of two sizes of rainbow trout (1.5 g and 3.8 g) within 96-h was 0.530 and 0.440 mg/L, respectively. Survival number of fish increased with increasing size of fish, but lethal dose was 0.28 g/g and 0.30 g/g for 1.5 g and 3.8 g of fish, respectively.