AbstractNitrogen-, sulfur-co-doped activated carbons were obtained from sulfur-modified and nitrogen-doped activated carbons that were prepared from waste medium density fiberboard. The electrochemical capacitive performance of the activated carbon samples obtained was investigated in 7.0 M KOH electrolyte. The morphology, structure, and surface properties of the samples were investigated by field emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM), N2 adsorption, X-ray photoelectron spectroscopy (XPS), and elemental analysis. The S-doping could be tuned by controlling the dosage of sulfur sublimed. Because of the introduction of sulfur functional groups, the prepared carbons exhibited better conductivity and higher specific capacitance, reaching 264 F/g under a current density of 50 mA/g and a 7.0 mol/L KOH electrolytic solution. A mechanism for improving the conductivity and capacitive performance of sulfur functional groups on activated carbons was discussed.