Cotton fabric has been processed into hierarchically porous carbon with a two-step chemical-free method, i.e. carbonization in nitrogen and controlled thermal oxidation in air. By optimizing thermal oxidation temperature, large surface area of 777 m2/g could be achieved in cotton fabric derived carbon. The processed carbon remained the micron-meter tubular structure (same as cotton fiber), while meso-/micro-pores were also generated on tube wall. This uniquely structured porous carbon was then doped with nitrogen via a thermal pyrolysis process by using melamine as nitrogen source. The nitrogen doping level was controlled by adjusting the mass ratio of melamine and porous carbon. The nitrogen content in the doped porous carbon could reach up to 9.0 atom% without sacrificing the porous structure and surface area. The nitrogen doping significantly improved the electrochemical capacitance up to 180 F/g at 0.5 A/g, which is 74% enhancement compared to the nitrogen-free carbon (104 F/g). Both origin carbon and nitrogen doped carbon show excellent cycling stability that 95% of the capacitance could be remained after 5000 charge-discharge cycles. Display omitted