Furoic acid (FA) is a useful bio-chemicals, which can be used in the production of pharmaceuticals, food additives, flavors, industrial chemicals, biofuels, etc. Oxidation of furfural to FA has been carried out by a thermal catalytic method, but photocatalytic oxidation protocol has not been reported yet. Here, g-C3N4-supported Ag nanoparticles (Ag NPs) catalysts with different Ag loading were synthesized and used for the photocatalytic oxidation of furfural to FA under visible light irradiation. The physicochemical and photoelectrochemical properties of the catalysts were systematically investigated by XRD, TEM, XPS, UV–Vis diffuse reflectance spectroscopy (UV–Vis DRS), photoluminescence, etc. Compared with the pristine g-C3N4, Ag-CN(N2 + H2) was found to have better photocatalytic performances in the aerobic oxidation of furfural under visible light irradiation, and the conversion can reach 82 % with a FA yield of 30 %. Importantly, the loading of Ag NPs has a significant effect on the photoelectrochemical properties. Specifically, 0.5 % Ag NPs loading maximized the photocurrent response, indicating that the loading of Ag NPs enhances charge separation and migration under visible light excitation. The introduction of Ag NPs also led to a significant decrease in electrochemical impedance, which promoted the rate of electron transfer at the interface, further confirming the improved photocatalytic efficiency. The addition of Ag NPs broadens the solar absorption and promotes the separation/transport of photo-generated carriers to form “hot electrons”, and provides the active species for furfural oxidation. The reasonable reaction mechanism of the photocatalytic oxidation of furfural to FA was elucidated. This work offers a novel method for the oxidation of furfural to FA in a mild and green way.