Nitrogen and oxygen-codoped carbon nanospheres were prepared by adopting sodium alginate (SA) as the carbon precursor in the presence of polyaniline (PANI) through direct carbonization process. A typical sample (PANI/SA-800) obtained at the carbonization of 800 degrees C shows regular a spherical shape (similar to 130 nm in average diameter) and a relatively rich oxygen (11.71 at.%) and nitrogen (3.48 at.%) doping. When PANI/SA-800 is used as an electrode material for electrochemical capacitor, a high specific capacitance of 627 F g(-1) at a current density of 1 A g(-1) in 3 M H2SO4 aqueous electrolyte is achieved. Furthermore, the electrode also displays exceptional cycling stability for 10,000 charge/discharge cycles with retention ratio up to 224.9% in acidic electrolyte at a high current density of 7 A g(-1). The renewable, cost-effective, and high electrochemical performance nitrogen and oxygen-codoped carbon nanospheres provide a promising candidate for advanced supercapacitor electrodes.