A novel BiOI/Ag₂CO₃ composite was synthesized through the co-precipitation method and well characterized by X-ray diffraction, Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy, scanning electron microscopy, transmission electron microscopy, energy dispersive X-ray spectroscopy, UV-vis diffuse reflectance spectroscopy and photoluminescence spectroscopy. Its photocatalytic activity was evaluated for degrading various pollutants (rhodamine B, methylene blue, methyl orange) and phenol aqueous solution. Experimental results indicated that Ag₂CO₃ nanoparticles anchored on the BiOI sheet surface promoted the enhanced photocatalytic activity. Moreover, when the mass ratio of BiOI in BiOI/Ag₂CO₃ composites was 20%, the as-prepared BiOI/Ag₂CO₃ (20 wt%) composite exhibited the optimal photocatalytic activity for degrading rhodamine B; its rate constant was approximately 6.75 and 4.3 times higher than the separate BiOI and Ag₂CO₃. The enhanced photocatalytic performance could be attributed to the heterojunctions between BiOI and Ag₂CO₃. Furthermore, the possible mechanism for photodegradation over the BiOI/Ag₂CO₃ composite is proposed.