In this work, a low-cost, high-performance, and environmentally friendly metal-free electrocatalyst based on N-doped carbon nanosheets (NCNs) was fabricated via the one-step pyrolysis of cheap corn starch and urea for the oxygen reduction reaction (ORR) in alkaline and acidic media. The results indicate that the nitrogen could be simply embedded into the carbon nanosheets by pyrolysis process. The effects of annealing temperature and raw material on NCN’s structure and electrocatalytic properties were investigated to optimize the preparation process. The results show that the total nitrogen content decreases while Brunauer–Emmett–Teller (BET) surface area, crystallization degree, graphitization degree, and electrical conductivity increase with the increase of pyrolysis temperature from 800 to 1000 °C. The measurements on the ORR activities by rotating disk electrode (RDE) in alkaline media (0.1 M KOH) and acidic media (0.5 M H₂SO₄) were investigated, and a nearly four-electron reaction pathway was observed. In comparison to commercial 20 % Pt/C catalyst (Pt/C), NCN exhibited excellent ORR electrocatalytic activity, methanol tolerant ability, and stability, making them promising metal-free alternative to Pt-based cathode catalysts in fuel cells. In addition, the findings obtained from this study may provide a scalable fabrication method for preparation of such low cost and high-efficiency metal-free oxygen reduction electrocatalyst derived from cheap biomass-based molecules.