A new electrochemical sensor has been developed based on the reduced graphene oxide (RGO)/polypyrrole (PPy)/zinc oxide (ZnO)/gold (Au) nanoparticles nanocomposite modified glassy carbon electrode (GCE) for simultaneous determination of ascorbic acid (AA), epinephrine (EP), and uric acid (UA). The morphology and structure of Au/ZnO/PPy/RGO nanocomposites were characterized by field emission scanning electron microscopy (FE-SEM), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (CPS) and Raman spectroscopy. The Au/ZnO/PPy/RGO/GCE-based sensor exhibited excellent electrocatalytic activity and high stability for determination of AA, EP, and UA. The prepared electrode separates the oxidation peak potential of AA-EP by 130 mV, and EP-UA by 150 mV, while the bare GCE cannot resolve them. Simultaneous determination of these species in their mixture solution showed a wide linear response 2-950 mu M, 0.6-500 mu M and 1.0-680 mu M for AA, EP, and UA, respectively. The detection limits of AA, EP, and UA were also calculated as 0.16, 0.06 and 0.09 mu M (S/N = 3), respectively. In addition, the proposed sensor shows good selectivity and stability along with good precision and consistency.