Design and fabrication of highly active photocatalysts under visible light irradiation are one of hotspots in the field of photocatalysis. In this paper, mesoporous AgInO₂ nanostructures have been synthesized through a combined sol-gel and ion exchange process. Thermogravimetric analysis-differential scanning calorimeter (TGA-DSC), X-ray diffraction analysis (XRD), field emission scanning electron microscopy (FESEM), N₂ adsorption-desorption and ultraviolet-visible (UV-vis) analysis technologies are used to investigate the effects of preparation condition on the microstructure of the AgInO₂. The photocatalytic performances have been evaluated by degradation of the formaldehyde under visible light irradiation. The results demonstrate that the mesoporous AgInO₂ is a delafossite structure with the uniform size about 200-500 nm and nitrogen adsorption- desorption type IV isotherms, the absorption edge of AgInO₂ lies between 500nm and 600 nm in the visible light scope. As-synthesized AgInO₂ exhibited remarkably high photocatalytic activity of 93.97% in decomposing formaldehyde for 180 min. These results provide a basic experimental process for preparation novel photocatalyst of AgInO₂, which will possess a broad prospect in terms of the applications in improving indoor air quality.