In this work, graphitic carbon nitride (g-C₃N₄) supporting finely dispersed Au nanoparticles is developed as a simple and efficient photocatalyst for H₂O₂ production under visible light irradiation. Au nanoparticle cocatalyst remarkably enhances photocatalytic activity of C₃N₄ for H₂O₂ production. Due to the inert nature to catalyze the decomposition of H₂O₂, Au/C₃N₄ also exhibits stable H₂O₂ evolution rate. It is of great interest that the maximal H₂O₂ production activity is reached at the loading amount of Au as low as 0.01%, revealing the great catalytic efficacy of highly dispersed Au cocatalyst during the photocatalytic H₂O₂ synthesis and the possibility to produce concentrated H₂O₂ using C₃N₄ with extremely low Au loading amount. The in situ electron spin resonance studies reveal that the H₂O₂ is produced through direct 2e⁻ oxygen reduction over Au/C₃N₄ photocatalyst.