Abstract: Various graphitic carbon nitride (g-C₃N₄) materials having nitrogen defects were synthesized by adding NaHCO₃ during the thermal polymerization of melamine. The as-prepared g-C₃N₄ samples were characterized by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), nitrogen adsorption-desorption, X-ray photoelectron spectroscopy (XPS), UV-visual diffuse reflectance spectroscopy (UV-vis DRS) and photoluminescence spectroscopy (PL); their photocatalytic activity in the degradation of Rhodamine B (RhB) under visible light irradiation was investigated. The results demonstrated that the unique nitrogen defects in g-C₃N₄ play an important role in broadening the absorption of visible light and enhancing the separation of electron-hole pairs. The photocatalytic activity of g-C₃N₄ with nitrogen defects is enhanced greatly; the RhB removal rates over the CNK0.005, CNK0.01, and CNK0.05 photocatalysts in 30 min reach 79.8%, 100.0% and 87.6%, respectively. In contrast, the pristine g-C₃N₄ free of nitrogen defects only gives an RhB degration rate of 59.8% under the same reaction conditions.