Background: Water contamination due to insecticides, often generates dangerous results for consumers. Immoderate consumption of insecticides in neighboring farms contaminates rivers. Assessment of residue of phosphorus insecticides which are used in farms near rivers can play a key role in preventing probable poisonings and aquatic ecosystems polution. Methods: In this case control study, water of three permanent rivers in Bushehr province and urban water pipe network of Bushehr city were assessed in different months in 2004-2005 and 216 samples were collected on the whole. In each river,three stations were used for sampling. After the sampling, extraction processes were accomplished using solvents such as: acetone, methylen-chloride and benzene. For detection and measurement of TLC Scanner apparatus was used. Results: Residues of diazinon and malathion were found in water of the three rivers in spring and summer. And in other seasons the rate of residues were very low or zero. The statistical analysis of the results through one-sidedanalysis variance, showed that diazinon and malathion residues in the water of the surveyed rivers in different months had significant difference (p 0.05), while malathion residue was significant (p <0.05). Conclusion: In the first and second months after applying the two insecticides, their residues level in all three rivers of Mond, Shahpour and Dalaky are more than acceptable contamination level, the higher levels belong to diazinon. Precautions must be considered in using the water for drinking purposes and also using aquatic foods which are provided from these rivers.