The present invention relates to a nanostructural substance constituted from primary particles having a particle diameter of not more than 30 nm. In the nanostructural substance of the present invention, the primary particles have a small particle diameter, and a contact surface between the primary particles is small. In particular, since the nanostructural substance of the present invention has a large content of molecules existing at the surface thereof and, therefore, a high surface energy as compared to simple agglomerated particles, it is expected to more remarkably exhibit functions of the compound constituting the primary particles.In addition, titanium oxide particles constituted from the nanostructural substance comprising primary particles having a small particle diameter and a small contact area therebetween according to the present invention exhibit a high catalytic activity and can be suitably used, in particular, as a photocatalyst.