The raw titania pulp was heated from 350 up to 700°C and the impact of TiO 2 properties on the photocatalytic decomposition of acetaldehyde under UVVis light was investigated. The physico-chemical parameters such as BET surface area, extent of surface hydroxylation, phase composition and size of TiO 2 crystallites, were measured. It appeared that low-hydroxylated TiO 2 prepared at 400°C with relatively high BET surface area (106 m 2 /g) and the crystallized anatase phase was the most active for the acetaldehyde decomposition. High hydroxylation of TiO 2 surface and the presence of amorphous TiO 2 slowed down the photocatalytic process in the gas phase. On the other hand, high concentration of OH groups on TiO 2 surface favored the generation of a high amount of OH radicals in an aqueous environment under UV irradiation. A sufficient amount of hydroxyl groups adsorbed on TiO 2 surface is needed to facilitate electron-hole separation and OH radicals formation. On the other hand, an excessive content of these groups results in the creation of a barrier for adsorption of acetaldehyde and thus deteriorates photocatalytic process. Additionally, the high concentration of hydroxyl groups on TiO 2 surface could accelerate recombination of radicals and reduce its photocatalytic efficiency in the gas phase.