For silica particles of two different sizes (0.9 and 3.2 mu m), TiO2 coating was performed using the sol-gel method. The results showed that size of primary TiO2 particles that accumulated on the silica surface was essentially the same regardless of the silica particle sizes. Reduction in specific surface area of TiO2-coated silica particles after calcination was observed to the same extent for both cases. Activity of the TiO2- coated silica particles was evaluated by photocatalytic decomposition of 2,4-dinitrophenol. The decomposition rate constant for both support sizes was proportional to the surface area of the anatase phase of TiO2 coated on silica particles. The decomposition rate constant was also essentially the same for both particle sizes. It was found that the silica particle size had a small effect on the surface morphology of the TiO2- coated silica particle and its photocatalytic activity.. (c) Koninklijke Brill NV, Leiden and Society of Powder Technology, Japan, 2008