Nitrogen-doped and nitrogen and oxygen codoped carbon nanobelts (CNBs) (denoted as N-CNBs and N-O-CNBs, respectively) are respectively obtained by pyrolyzing the self-aligned polypyrrole (PPy) NBs and Se@poly(2-methoxy-5-nitroaniline) core@shell nanowires. Particularly, the uniform size, unique nanostructure, and well-defined edges of the PPy NBs result in the uniform size of the doped CNBs with an extraordinarily high N doping level (≈16 at%), especially the very large concentrations of the redox active pyridinic (9 at%) and pyrrolic N (3.5 at%) species. Furthermore, the precursors in highly self-aligned, dense arrays give rise to a very high packing density for the N-CNBs and N-O-CNBs. These incomparable features provide not only appropriate pathways for the introduction of pseudocapacitance via rapid Faradaic reactions and enhancement of volumetric capacitance but also structural design and synthesis approach to new types of nanostructured carbon. Notably, the N-CNBs obtained at the pyrolysis temperature of 800 °C (N-CNB8) in symmetric electrochemical cells deliver a specific capacitance of 458 F g and ultrahigh volumetric capacitance of 645 F cm in aqueous solution, which are among the best performance ever reported for carbon-based supercapacitive materials.