A novel nanocomposite of hexagonal cobalt oxide nanosheets (HCONS) homogeneously dispersed on a carbon matrix of reduced graphene oxide (RGO) and multiwall carbon nanotubes (MWCNTs) has been developed. The HCONS@RGO@MWCNT nanocomposite was prepared successfully via a hydrothermal process followed by calcinations for the individual and simultaneous non-enzymatic detection of ascorbic acid (AA), uric acid (UA), and dopamine (DA). The morphology and structure of the HCONSs and synthesized nanocomposite were analyzed by X-ray photoelectron spectroscopy (XPS), field emission scanning electron microscopy (FESEM), energy dispersive X-ray spectroscopy (EDX), and Raman spectra. The electrochemical performance of the nanocomposite was investigated using cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). Under optimized conditions, the simultaneous determination of the AA, DA, and UA were examined using differential pulse voltammetry (DPV) with linear ranges of (12.5−1382), (1.6–23.6), and (46.5–806.5) μM, and lower detection limits of 12.5, 0.012, and 1.5 μM (S/N=3), respectively. The proposed electrode exhibited an excellent selectivity, long-term stability, and good reproducibility. Therefore, the developed nanocomposite is a promising material for non-enzymatic electrochemical sensors.