The photoassisted degradation of n-butyltin chlorides in air-equilibrated aqueous TiO2 suspension has been studied. Several factors affecting the degradation rate, such as the extent of adsorption on the surface of catalyst particles and the effect of pH values, were examined. Particular interest is focused on the TiO2-assisted photodegradation of n-butyltin species. The simultaneous photodeposition of tin oxides/metallic tin on the TiO2 surfaces is also addressed as a route to form surface-complexed semiconductors. A mechanism consisting of interfacial trapping of a photogenerated electron-hole pair can explain the observed photoassisted degradation of n-butyltin species and the simultaneous photodeposition of tin onto the TiO2 surface. The results are compared with those, previously reported, on the photolytic degradation of these species in water.