The Ti/Al2O3 (1 ($) over bar 1 0 2) interface formation has been investigated by X-ray photoelectron spectroscopy and Auger electron spectroscopy (AES). The results showed that when an active metal titanium was evaporated on to a room-temperature Al2O3 (1 ($) over bar 1 O 2) surface in ultrahigh vaccum, a Ti/Al2O3 interface region of about 200 nm was formed, and in the first several monolayers of titanium, the titanium was oxidized due to the active oxygen anions on the surface. Therefore, the pure Ti/Al2O3 interface was replaced gradually by a titanium oxides/Al2O3 interface, which has a stronger interaction than the former. The change of shape of the photoemission lines and the shift of binding energy of aluminium, oxygen and titanium with increasing coverage of titanium showed that the formation of the Ti-O bond at the interface is due to titanium transferring its electrons to Al3+ via O2- anions in the Al-O bond, whereby the Al3+ was reduced to metallic aluminium, Al-0. The AES intensity profile also proved the existence of the reduced species Al-0. This suggests that the reaction layer consists of a multiphasic mixture : the Ti-O type phase, the (Ti, Al)(2)O-3 phase and metallic aluminium phase.