A novel poly(malachite green)/graphene nanosheets-nafion (PMG/GNs-NF) composite film-modified glassy carbon electrode was developed to indirectly detect methyl parathion (MP). p-nitrophenol, the alkaline hydrolysis product of MP, was successfully determined at a relatively lower potential using this modified electrode due to the excellent electrocatalytic activity of PMG/GNs-NF composite film. The presence of GNs in the composite film enhanced the stability of PMG and increased the electron transfer rate. The kinetic parameters of modified electrodes were studied. What is more, the optimum experimental parameters affecting response were selected in terms of pH, accumulation potential, accumulation time, scanning cycles during polymerization of malachite green, and alkaline hydrolysis conditions. Under optimum conditions, the chronoamperometric response current was proportional to MP concentration over the range from 0.02 to 1.5 mu M with a low-detection limit of 2.0 nM. Finally, the sensor was applied for the determination of MP in real samples, and the results were satisfactory with recoveries from 97.20 to 104.53 %. Due to its simple preparation, good reproducibility, and stability, this developed modified electrode provides a new platform for the detection of organophosphate pesticides.