Abstract: A particulate titanium oxide is obtained which has a large specific surface area and a high crystallinity with few internal defects, and thus a high photocatalytic activity as a photocatalyst is expected. Particulate titanium oxide in which the particles are box-shaped polyhedra is used as the photocatalyst. The particles are each a box-shaped polyhedron composed of one or more titanium oxide single crystalline polyhedron. When this single crystalline polyhedron has a flatness ratio of 0.33 to 3.0, the crystallinity is even higher. The particulate titanium oxide typically has a rutile transition ratio R(700-24) of not more than 7.5% and a rutile transition ratio R(500-24) of not more than 2.0%. Titanium oxide particles of these shapes are manufactured by feeding titanium tetrachloride vapor and oxygen into a reaction tube made of silica glass and applying heat from outside the tube to effect thermal oxidation.