In this study the distribution and accumulation of diazinon, malathion and azinfos methyl in mullet fish Liza aurata, caspian white fish Rutilus frissi kutum and common carp fish Cyprinus carpio from five estuaries along the Caspian Sea was investigated. Also, the effect of pesticides concentration on the acetylcholinesterase enzyme (AChE) in fish species was studies. Pesticides concentration varied with fish species, sampling station and toxin type. The results indicate that the pesticides concentration varied from 0.01 to 0.16 mg/kg for diazinon, 0.01 to 0.15 mg/kg for malathion and 0.05 to 0.36 mg/kg for azinfos methyl in three fish species. There was significant difference between different toxin concentrations in fish species, (P < 0.05), and the order of toxic concentrations was as follows: azinfos methyl > diazinon > malathion. There was significant difference in toxin concentrations between three fish species, and the highest toxins concentrations were absorbed in detritivores fish (L. aurata), followed by herbivorous fish (C. carpio) and carnivore fish (R. kutum). The results confirmed that toxins bioaccumulation in fish species is strongly controlled by habitat and feeding habits.