Abstract: Photo-catalytic TiO₂ was prepared from tetraisopropyl titanate (TPT) in supercritical ethanol. It was found that TPT in supercritical ethanol could be effectively converted into the anatase-form of TiO₂ crystallites. The anatase-form of TiO₂ as a photo-catalyst was evaluated for its adsorptivity and subsequent photo-catalytic activities on formaldehyde, one of the harmful air pollutants in the environment. As a result, the supercritically treated TiO₂ had a high decomposing ability. Under the same condition, the experiment was repeated for 5 times,and photocatalysis of the samples did not decrease. This indicated that the supercritical treatment was effective to prepare photo-catalytic TiO₂, which was feature by stability, longevity and high photo-catalytic decomposition of formaldehyde for environmental cleaning. Meanwhile, unlike conventional chemical reaction, which is complex and time-consuming, supercritical treatment is easy to operate, saving both time and labor.