A novel photocatalyst In(OH)₃ was synthesized by peptization of a colloidal precipitate under ultrasound radiation. The photocatalyst was characterized by N₂ adsorption, XPS, XRD, UV–vis DRS, and FTIR technologies. The photocatalyst sample is highly photoactive and stable for gas-phase removal of benzene under UV irradiation, even in dry O₂ atmosphere. Both the conversion of benzene and the mineralization yield are notably accelerated, as compared to the widely used photocatalyst – titania (Degussa P25). In(OH)₃ is active even after 30h of photoreaction. The maximal conversion and mineralization ratio of benzene achieved are 33.4% and 56%, respectively, which is much higher than that obtained with TiO₂ (9.5% and 24%). The high activity and durability of the In(OH)₃ can be ascribed to the high hole oxidation potential and carbon deposits formed uneasily on the catalyst surface.