In this study, a method for extraction and preconcentration of trace amounts of organophosphorus pesticides (OPPs) in environmental water using magnetic solid phase extraction (magnetic-SPE) followed by high performance liquid chromatography (HPLC) with UV detection was developed. The magnetic carbon nanotube adsorbents (Fe3O4/CNT) were synthesized by grafting carbon nanotubes to magnetic Fe3O4 particles by a facile hydrothermal method. The synthesized Fe3O4/CNT nanoparticles were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), Fourier transform infrared spectroscopy (FTIR), and vibrating sample magnetometer (VSM). These nanoparticles were used for extraction and preconcentration of OPPs (fenitrothion, profonofus, and ethion) in environmental water samples at low concentration. The influence of four variables including adsorption time, weight of sorbent, salt addition, and pH in the extraction process were predicted and optimized by Response Surface Method (RSM). Under optimized conditions, it showed good linearity between 0.5-10, 0.5-10, 0.5-30 ng ml-1 with determination coefficients (R2) of 0.993, .0995, and 0.994 for extraction of ethion, profonofus, and fenitrothion, respectively. Limit of detection (LOD) for extraction of ethion, profonofus, and fenitrothion were also evaluated under optimized conditions as 0.124, 0.097, and 0.108, respectively. The analysis also showed good reproducibility with the RSD values 4.4, 2.7, and 4.5 at the 10 ng ml-1 level (n=5) for ethion, profonofus, and fenitrothion, respectively.