Abstract: The design, synthesis, characterization, and applicability of magnetic molecularly imprinted polymer (MIP-APTES-MNP) as a selective sorbent for the extraction of diazinon from plasma samples were investigated. To design more sophisticated polymers, appropriate monomer, crosslinker, polymerization solvent, and ratio of monomer to template and crosslinker were selected by a methodology based on density functional theory calculations. The sorbent particles were characterized by Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), thermogravimetric analysis (TGA), vibrating sample magnetometry (VSM) and X-ray diffraction (XRD). The extraction of a few organophosphates, including dimethoate, dichlorvose, malathion, fosalon, diazinon, chlorpyrifos, and ethion, were evaluated to estimate possible interfering effects. Equilibrium isotherms and the kinetics of extraction were studied to reveal the mechanism and rate of adsorption. A UHPLC-UV method was also developed to monitor OPPs on a short C18 column using H2O : acetonitrile as mobile phase during isocratic and gradient elution steps. The synthesis of the polymer was carried out under deoxygenated condition at molar ratio 1 : 5 : 18 of template : monomer : cross-linker. Sorbent characterization results showed that the particles were of nanosize range and adsorption was best fitted on Langmuir model with pseudo-first-order kinetics. The maximum enrichment capacity, Langmuir constant, and limit of detection for diazinon were calculated as 5, 0.937 mg L-1, and 5 μg L-1, respectively. The highest and lowest saturated adsorption capacities of the sorbent for OPPs were found to be 92% and 23% for diazinon and ethion