Novel Na3MnCO3PO4 (NMCP)/reduced graphene oxide (rGO) nanocomposite was successfully synthesized via one-step hydrothermal method. The produced materials were characterized by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), Raman spectroscopy, field emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM), thermogravimetry (TG), galvanostatic charge/discharge test and inductively coupled plasma optical emission spectroscopy (ICP-OES). Obtained results indicate the formation of ∼25nm NMCP nanoparticles randomly distributed on rGO sheets. As a promising cathode material for Na-ion batteries, the hybrids deliver gravimetric discharge capacities of 98.3mAh per gram of electrode (156.0mAh per gram of NMCP) and 114.0mAh per gram of electrode (180.9mAh per gram of NMCP) at C/30 and C/100 rates, respectively. The obtained gravimetric capacities indicate 39% and 52% improvement at C/30 and C/100 rates, respectively, in comparison with the highest corresponding values reported in the literature. The synergy arising from the formation of fine NMCP nanoparticles and NMCP/rGO hybridization is responsible for the achieved higher capacities.