Development of an effective electrochemical sensor for the sensitive detection of antibiotics in food, pharmaceutical formulations and biological liquids is of current interest. We have looked at possibility of rapid detecting sulfamethoxazole (SMZ), an antibiotic of the sulfonamide family, using a composite of reduced graphene oxide, polydopamine and copper nanoparticles as a modified electrode. The important parameters for synthesis of the composite were identified. Using the modified sensor, linear range of SMZ concentration is 4 - 80 μM, with R2 = 0,9893 and LOD of 1.12 M. Furthermore, the modified electrodes were used for the examination of the SMZ content in a commercial product, with reasonable recover