A novel Ag/AgAlO2 composite has been prepared by a two-step method. The results indicated that the photocatalytic activity for the decomposition of formaldehyde with visible light irradiation of Ag/AgAlO2 is enhanced by 22.8% compared to that using pure AgAlO2. The enhanced performance is caused by the synergistic effect of heterostructure Ag/AgAlO2 composite.