Nitrogen-doped plasma treated graphite is synthesized by using ammonium hydroxide and ambient plasma for supercapacitor applications. Nitrogen is doped 9 wt%, and electrochemical active surface area is increased five times, compared to the precursor graphite. Electrochemical impedance is also dramatically reduced from 296 to 34 Omega at 100 Hz. The specific capacitance is finally improved from 27 Fg(-1) to 399 Fg(-1) at 50 mVs(-1), demonstrating high energy density of 40.4 Whkg(-1) when its power density reaches to 617 Wkg(-1). The capacitance retention was 91% after 1000 cycles, revealing high cyclic stability and reliable performance for the supercapacitor applications.