Silica-embedded titania photocatalyst (X-silica/titania, X denotes at.% of silicon) of improved photoactivity was prepared by the sol-gel technique. The photoactivity of the X-silica/titania particles was increased by increasing the silica content and reached a maximum. The highest photoactivity was obtained when silica content was 30% and five times higher than that of Degussa P25. The embedding of amorphous silica into nanophase titania matrix helped to increase the thermal stability of titania which suppressed the formation of anatase into rutile and made it possible to calcine the silica/titania particles at higher calcination temperature. This high temperature heat treatment resulted in the high crystallinity of the silica/titania particles. Surface area of X-silica/titania particles was monotonically increased by increasing the silica content. The average pore size and pore volume, however, has a maximum at 30%, at which mesopores larger than 30 nm were observed. Therefore, we concluded that the large pore size and pore volume were responsible for the optimum composition of silica to titania. The enhanced photoactivity of silica-embedded titania particles was achieved by simultaneously increasing both the surface area and the crystallinity through embedding amorphous silica into titania. (C) 2000 Elsevier Science B.V. All rights reserved.