Ultra fine TiO2 particles which dispersed in various organic solvents were synthesized through hydrolysis of a titanium alkoxide to form colloidal TiO2 particles, followed by modification of the colloidal particles with a hydrophobic coupling agent, The organic solvent solutions of the synthesized TiO2 particles were transparent and had high colloidal stability. Photochemical properties of the TiO2 particles in organic solvents were studied : namely how Ti3+ species were formed in the particles and accumulated in them; and how the particles were photocatalytically active for oxidation of I- and reduction of methylene blue and Ag+. From comparative studies of the photocatalytic reactions, the TiO2 particles are found to have higher photocatalytic activity than commercially available anatase and rutile ponders.