A novel Ag3PO4/multiwalled carbon nanotube (Ag3PO4/MWCNT) composite has been prepared by a simple precipitant approach. The obtained samples were characterized by X-ray diffraction, scanning electron microscopy, energy-dispersive X-ray, UV-Vis diffuse reflectance, and Raman spectroscopy. It is found that the MWCNTs are well deposited on Ag3PO4 nanoparticles. The Ag3PO4/MWCNT composite with MWCNT content of 1.4 wt% exhibits optimal photocatalytic activity under visible light. The rate constant of MO degradation over Ag3PO4/1.4 wt% MWCNT is 5.84 times that of pure Ag3PO4. Compared with pure Ag3PO4, the incorporation of MWCNTs not only significantly enhances the photocatalytic activity but also improves the structural stability of Ag3PO4, suggesting that the synergistic effects take place in the composite. The improvement is attributed to the conductive structure supported by MWCNTs, which favors electron-hole separation and the removal of photogenerated electrons from the decorated Ag3PO4. A possible photocatalytic mechanism of the (Ag3PO4MWCNT)-M-/ photocatalyst was assumed as well.