Water Pollution by pesticides is one of the major environmental problems that observe in the surface water of Gilan province because of increasing usage of pesticide due to agriculture development and resitance pest. Polroud River is one of the most important rivers in the eastern of Guilan. There are vast paddy fields in this catchment and a large amount of the organophosphorous pesticides wich drained to the Caspian Sea. Diazinon is one of the well-known pesticide in this area in order to control of ChiloSuppressalis.In current research, the concentration of Diazinon in water, sediment and Sambucusnigra was analysed, Samples were gathered from five stations during two seasons, spring (June) and summer (July, August)of 2012. The water sampels were extracted by solid phasetechnique and then all extracted samples were analyzed by GC-NPD.Finally,obtained data were analyzed by using ANOVA and T-TEST statistical methods.According to the analysis results, Diazinon concentration was negligible in the water, plants and sediment samples during the spring . The maximum concentration of Diazinon(0/75 (l/ug in water sampels was observed in station 3 at summer.Based on the statistical analysis, there was a significant difference between Diazinon concentration in water, plants and sediment samples in summer.