The pony-size Cu nanoparticles confined in mesoporous C-N were directly synthesized by chemical vapor deposition (CVD) method using floating Cu atoms. The mesoporous C-N with high surface area not only stabilized the dispersed Cu nanoparticles but also improved the electrocatalytic activity of the Cu by changing the electronic structure of Cu. Combining the strong interaction between Cu nanoparticles and mesoporous C-N and the quantum size effect of Cu nanoparticles, the obtained Cu@C-N exhibited the catalytic activity superior to the reported Cu nanoparticles-based catalysts and commercial Pt/C-JM catalyst with a half-wave potential of 0.84 V for oxygen reduction reaction (ORR) in alkaline media. Additionally, it also showed remarkable catalytic stability and excellent methanol-tolerant property during the ORR process.