The relationship between the hydrolysis conditions of titanium tetraisopropoxide (TTIP) and the thermal transformation of the hydrolysis products was investigated as a part of study on the properties of TiO₂ formed by the hydrolysis of titanium alkoxide. The amorphous products formed under the HNO₃ and HCl acidic conditions transformed to anatase at about 200°C. This temperature was about 100°C higher than that of the amorphous products formed with neutral water, and was not correlated with the H₂O/TTIP molar ratio. On the other hand, the anatase-rutile transformation was significantly accelerated under the acidic condition. In particular, the single-phase rutile particles which were needle-shaped and about 0.1μm in length were formed at room temperature when the concentrations of acids were more than 6wt% for HNO₃ and more than 4wt% for HCl at the molar ratio of H₂O/TTIP=20. In the case of the hydrolysis product formed under H₂SO₄ acidic condition, on the contrary, the temperatures of the amorphous-anatase and anatase-rutile transformations were higher than those of hydrolysis products with neutral water, and its values were 300 and 700°C, respectively.