In this research residues concentration relationship of 3 organophosphorus pesticides and 11 organochlorine pesticides in water and sediment in different seasons in the Siahrud River from Qaemshahr (Mazandaran, Iran) were studied. Water and sediment from Qaemshahr Siahrud River was sampled from 7 stations in 3 seasons and the concentration of pesticides was measured by GC/ECD device. Water samples with a concentration of DDTs from the LOD to 0.050 μgr/l and cyclodiene from the LOD to 0.020 μgr/l and HCH from the LOD to 0.78 μgr/l and organophosphorus pesticides to 1.86 μgr/l and sediment samples DDT from LOD to 0.080 μg/g dw and cyclodiene to 0.04 HCH to 0.17 μg/g dw and organophosphorus pesticides was to 3.29 μg/g. Effect of seasons on the concentration of pesticides in water and sediment showed the highest concentration for all pesticides in summer and all water and sediment samples at all stations and in three seasons. Organophosphorus concentrations were higher due to high current consumption and very low their half-life in the water. The sediment is causing enormous difference in the concentration of pesticides in the summer with a concentration in autumn and spring.