The synthesis of heteroatom-doped graphene nanosheets is one of the recent trends to improve the energy storage capabilities of graphene in devices such as supercapacitors. We report on the optimized fabrication of sodium-nitrogen-phosphorus co-doped graphene sheets (Na/N/P-GNS) via a simple one-pot green method. The fabricated Na/N/P-GNS were characterized using X-ray diffraction (XRD), Raman spectroscopy, thermogravimetric analysis (TGA), FTIR, scanning electron microscopy (FESEM), X-ray photoelectron spectroscopy (XPS), and transmission electron microscopy (TEM). Various electrochemical techniques were used to investigate the capacitance and performance of the prepared Na/N/P-GNS, including cyclic voltammetry (CV) at different potential scan rates and electrochemical charge/discharge at different current densities in 0.5 M H2SO4 aqueous electrolyte at room temperature. Na/N/P-GNS showed a maximum specific capacitance of 499 F/g at a scan rate of 1 mV/s, excellent cycling retention of 101% after 1000 cycles at 200 mV/s, and high energy density of 98.58 Whkg(-1). The high capacitance can be ascribed to the co-doping of Na, P and N and the one-pot synthesis methods that retain the graphene sheets unstacked. Based on the obtained capacitance, the fabricated Na/N/P-GNS would be a promising electrode material for supercapacitors.