Abstract: In this study, a small-sized CoNi bimetallic co-catalyst was synthesized in situ on g-C₃N₄ nanosheets using a simple chemical reduction method. The physicochemical properties of the prepared CoNi/g-C₃N₄ were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), UV-vis diffuse reflectance spectroscopy (UV-vis DRS), X-ray photoelectron spectroscopy (XPS), photoluminescence (PL) and electrochemical impedance spectroscopy (EIS). The photocatalytic degradation of RhB showed that the CoNi bimetallic co-catalyst could effectively improve the separation efficiency of photogenerated carriers in g-C₃N₄, thus enhancing the photocatalytic activity. The highest catalytic activity of CoNi/g-C₃N₄ was achieved when the molar ratio of CoNi was 1∶1, with a degradation rate of 0.01633 min⁻¹, which was 3.9 times higher than that of normal g-C₃N₄ under visible light irradiation. The photocatalyst maintained good photocatalytic activity after five cycles. The main active species of the reaction is the superoxide radical (\cdot \rmO^-_2 ).