Biochemical compounds play important roles in various biological processes and their determination in physiological fluids are necessary in the diagnosis and treatment of diseases. In this work a new biosensor is introduced based on glassy carbon electrode (GCE) modified with Cu 2 O nanocubes decorated o reduced graphene oxide (rGO) functionalized with 4-aminothiophenol (Cu 2 O-NC@f-rGO) for simultaneous determination of acetaminophen (AC) and codeine (COD). Morphological aspects, structure properties and electroanalytical behavior of Cu 2 O-NC@fr-GO/GCE electrode were studied using field emission scanning electron microscopy(FE-SEM), transmission electron microscopy(TEM), X-ray diffraction(XRD), electrochemical impedance spectroscopy(EIS) and cyclic voltammetry(CV). Also differential pulse voltammetry(DPV) was used for optimization of parameters such as pH, accumulation time, accumulation potential and DPV parameters the simultaneous determination of AC and COD. According to results, AC and COD were successfully determined by Cu 2 O-NC@fr-GO/GCE electrode; where calibration curve for COD was in the ranges of 0.2 -100 µM and for AC was in the range of 0.6 - 110µM. The detection limit for AC and COD were 0.04µM and 0.02µM ,respectively. The result illustrates the modified electrode can successfully applied for determination of AC and COD in blood serum and tablet.