A facile direct growth method was developed for the fabrication of Ag2CO3 nanoparticles on the surface of g-C3N4 at room temperature. The as-prepared g-C3N4/Ag2CO3 composites were characterized by X-ray diffraction, Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy, transmission electron microscopy with energy dispersion X-ray spectroscopy, UV-vis diffuse reflectance spectroscopy, and photoluminescence spectroscopy. The photocatalytic activities were evaluated by degrading Rhodamine B dye. The results indicated that Ag2CO3 nanoparticles with the size of 5-10 nm were finely distributed on the surface of g-C3N4 sheet, leading to the enhancement of the photocatalytic activity. And when the mass ratio of g-C3N4 to Ag2CO3 was 1:4, the as-prepared composites exhibited the optimum photocatalytic activity, which was approximately 8 and 3 times higher than pure g-C3N4 and Ag2CO3, respectively. The enhanced photocatalytic performance could be attributed to the synergetic effects between g-C3N4 and Ag2CO3, including the smaller particle size of Ag2CO3 and high charge separation efficiency of the photogenerated electron-hole pair. More attractively, the stability of Ag2CO3 was improved due to its highly dispersion on g-C3N4 sheet. In addition, based on the experimental results, the Z-scheme mechanism for the photodegradation over g-C3N4/Ag2CO3 composites was proposed.