TiO2-SiO2 composite oxides were prepared by rapid hydrolysis of a mixture of Ti(OPri)(4) and Si(OEt)(4) in ethanol with aqueous acetic acid. Photooxidation of propylene with O-2 was carried out over TiO2-SiO2 catalysts containing 5 and 75 mol% TiO2, and titanosilicate (TS-1). Propylene oxide was produced only over 5 mol% TiO2-SiO2 and TS-1, where Ti species are in a tetrahedral configuration. It was postulated that propylene oxide was formed by reductive elimination via C-O bond formation in a titanaoxacyclobutane produced from photoactivated Ti-O and propylene.