A glassy carbon electrode modified with magnetite nanoparticles dispersed in chitosan was employed as electrochemical detector for the determination of parathion in food samples by cathodic square-wave voltammetry. The modified electrode surface was characterized by scanning electron microscopy, cyclic voltammetry and electrochemical impedance spectroscopy. Under optimized experimental conditions, the square-wave voltammograms for parathion obtained with the proposed modified electrode exhibited a well-defined peak at -0.59 V, corresponding to the reduction of the nitro group to the hydroxylamine group. The resultant cathodic peak current was linear for parathion concentrations in the range of 0.34 to 4.46 mu mol L-1 (r = 0.997). The limits of detection and quantification were 0.187 and 0.567 mu mol L-1, respectively. The novel detector was successfully employed for the analysis of parathion in five food samples (carrot, orange, tomato, lettuce and rice) using the standard addition method. The results were statistically compared with data obtained using the UV-vis technique.