An interfacial mechanism for reactions between a Me-Ti thin film (Me=3d transition metals; Cu,Ni) and an A12O3 substrate is newly proposed. It has been clarified that Me3Ti3O (diamond cubic of Fd3m), which is formed as an intermediate phase in both the Cu-Ti/Al2O3 and Ni-Ti/Al2O3 systems, is responsible for the bonding between Me and A12O3. The solid-state reactions of the Me-Ti bilayer film/Al2O3 system were studied with Auger electron spectroscopy (AES) and X-ray diffraction (XRD) to clarify the interfacial reaction between Me-Ti and the A12O3 substrate. Me3Ti3O was observed at the interface between A12O3 and Me after annealing. Me3Ti3O was formed by oxidation of the Me-Ti compounds. The oxygen which reacted with the Me-Ti compounds has been found to be generated from the reduction of the A12O3 substrate.