Abstract: A graphene- based magnetic nanocomposite ( graphene- ferriferrous oxide, G- Fe3O4) was synthesized by one- pot solvothermal method and used as an effective adsorbent for the preconcentration of someorganophosphorus pesticide ( diazinon, parathion- methyl, pirimiphos- methyl, isocarbophos and quinalphos) in environmental water samplesprior to Gas Chromatography ( GC) detection. The method, which took the advantages of both high adsorption capacity of graphene and easy separation fromthe sample solution of Fe3O4, could avoid the time- consuming experimental procedures commonly involved in the traditional solid phase extraction such as centrifugation and filtrations.Various experimental parameters affecting the extraction efficiencies such as the amount of the magnetic nanocomposite, extraction time, salt concentration, and desorption conditions were investigated.The optimal adsorbent dosage was 20 mg, and the most appropriate extraction time was 15 min, and the most suitable salt concentration was 0.5%.What's more, the ideal elution was acetonitrile and 1.5m L was chosen as the elution volume.Under the optimum conditions, the linear correlation coefficient ranged from 0.9985 to0.9996.The limits of detection of the method were between 0.0002 and 0.009 ng / m L, the relative standard deviations ( RSDs) for five replicates ranged from 3.2% to 7.8%. The results indicated that as a magnetic solid-phaseextraction adsorbent, the graphene- ferriferrous oxide ( G- Fe3O4) had a great potential for the preconcentration of pesticides from liquid samples.