Diazinon is a pesticide that is commonly used in the rice fields of northern Iran The harmful effect of Diazinon and two anionic detergents were determined on Rutilus frisii kutum, individually and together on a laboratory scale. Fish were adapted to laboratory circumstances, distributed species wise in 500 litre tanks. Experiments were performed according to the TCR standard procedures. The LC50-96 h was 0.34 mg/l for Diazinon. The LC50-96 h in same species fingerlings were 4.69 and 12.24 mg/l under liquid and powder detergents, respectively. The LC50-96 h were 7.27 and 0.9 mg/l for a mixture of Diazinon and liquid detergent and a mixture of Diazinon and powder detergent, respectively. The result showed that the toxicity of the mixture of Diazinon and powder detergent was greater than other mixtures. Generally, the detergent concentration toxicity rate (LC50-96 h) in the ecosystem is less than the laboratory scale, but detergent can mix with some chemicals in the ecosystem and become stronger. The mortality rate will increase under this condition.