Abstract: In this work we report the feasible modification of graphitic carbon nitride (g-C₃N₄) polymer through a post-functionalization progress. The resultant photocatalyst exhibits boron doping and mesoporous structure with a high surface area of 125 m²/g, leading in an increased surface activity for photocatalytic water splitting reaction. X-ray diffraction, X-ray photoelectron spectroscopy, PL emission spectra and UV-Vis spectra were used to detect the properties of as-prepared samples. Based on X-ray photoelectron spectroscopy analysis, boron is proposed to dope in the g-C₃N₄ lattice. Optical studies indicated that boron doped g-C₃N₄ exhibits enhanced and extended light absorbance in the visible-light region and a much lower intensity of PL emission spectra compared to pure g-C₃N₄. As a result, boron doped g-C₃N₄ shows activity of 10.2 times higher than the pristine g-C₃N₄ for photocatalytic hydrogen evolution. This work may provide a way to design efficient and mesoporous photocatalysts through post modification.