Different pollutants have undesirable effects on aquatic ecosystems, detergent powder is one of the elements in the sewages so study on the effects of this factor on aquatic animals is crucial. The aim of the present study was to investigate acute effects of detergents as potentially dangerous additive to assess mortality effects of this product on some cultured fish. Silver Carp (Hypophthalmicthys molitrix), Common Carp (Cyprinus carpio), Goldfish (Carassius auratus) and Roach (Rutilus rutilus caspicus) were exposed to the 0, 2, 10, 20 and 40 mg L-1 of detergent powder. All experiments were done according the standard methods for 96 h exposure. LC50 was determined by probit analysis. The 96h toxicity tests showed 100% mortality at 40 mg L-1, and no mortality was observed in 5 mg L-1 for all species. LC50 of detergent powder in Goldfish (24.6 ± 0.32 mg L-1) was higher than other species, while silver carp (16.7 mg L-1) had the lowest one.