AgCl was incorporated with clay montmorillonite to improve the individual catalytic or adsorption performance. A green method was proposed to synthesize AgCl/montmorillonite composite by intercalating silver-ammonia complexes into the interlayers of montmorillonite followed by reacting with HCl vapor to in situ form AgCl particles on montmorillonite. The as-prepared samples were characterized by X-ray diffraction, scanning electron microscope, energy dispersive X-ray spectroscopy, transmission electron microscope, Brunauer-Emmett-Teller analysis, X-ray photoelectron spectra, and UV-vis diffuse reflectance spectrum. It was shown that AgCl not only intercalated into the interlamination of montmorillonite but also anchored on its exterior surfaces. AgCl on clay surface was cube-like particles, which were dominated by the higher activity of {1 0 0} planes. The photocatalytic activity of AgCl/montmorillonite (AgCl-Mt) composites were evaluated by degradation of azo dye Acid Red 18 (AR18) under UV-irradiation. AgCl in AgCl-Mt composites had an optimum amount. When 3CEC of silver-ammonia was used to prepare [Ag(NH3)(2)](+)-exchanged Mt, the obtained 3AgCl-Mt had the best activity. The degradation of 50 mL AR18 at pH 6 with 1 g L-1 of catalyst only needed 10 min. The low pH and dye concentration, and high catalyst loading favored the removal of dye. Moreover, the superoxide radicals and holes were found to be major reactive species responsible for the photocatalytic degradation of AR18. PL revealed that besides reducing the aggregation of AgCl and tailoring morphology of AgCl, montmorillonite also suppressed the combination of photogenerated electron-hole pairs, and thus enhanced the photocatalytic activity and stability. This study may offer an efficient approach for fabricating silver-halide-based composite photocatalysts for environmental cleanup.