We report a facile method to fabricate Bi₂MoO₆ nanosheet array exposed with {010} facets for the highly improved photoelectrochemical (PEC) property related to water oxidation. The nanosheet array film would provide large surface area, low resistance and exposed oxygen atoms, facilitating the electrons transport and charge separation. More importantly, the optimized Bi₂MoO₆ nanosheet array yields a photocurrent density of 220 μA/cm2, which is more than two orders of magnitude higher than that of conventional Bi₂MoO₆ particles (1.8 μA/cm²). Additionally, the nanosheet arrays were modified with ultrathin graphitic carbon nitride (g-C₃N₄) nanolayers as co-catalyst to enhance the photoelectrochemical activity. As expected, this unique photoanode yields a photocurrent density of 520 μA/cm² at +0.8 V (versus SCE) under visible light irradiation, which is 2.3 times higher than the pure Bi₂MoO₆ nanosheet film. The origin of enhanced photoelectrochemical activity of the co-catalyst modified film may be due to the large surface area, oriented electrons transport pathways and improved charge separation. These demonstrations clearly reveal that the rationally fabricating of high photoactive nanosheet array and coating ultrathin cocatalysts may serve an alternate strategy toward the development of highly efficient photoanodes for water splitting.