A 500 nm titanium film was deposited on a polished (1102) oriented sapphire (α-A12O3) substrate using electron beam evaporation under ultra high vacuum conditions. Isothermal furnace annealing has been used to cause the solid-state reaction between Ti film and sapphire substrate. Inter-facial reaction of Ti/α-Al2O3 was studied in detail from room temperature (RT) to 850 ℃ using XRD (including general and low incident angle X-ray diffractions), AES (Auger electron spec-troscopy, including the depth profile and the shape analysis of Auger spectra across the interface) and SIMS (Secondary ion mass spectrometry) etc. surface analysis techniques. It was found that at RT and after 300℃ 30 min. annealing, Al2O3 was reduced by titanium to produce metallic A1 accumulated at the interface. After 600 ℃ 30 min. annealing, Ti3Al and TiO2 were formed. After 850 ℃ 30 min annealing , the amount of Ti3A1 is increased with the temperature, at meantime the new phases of a number of titanium oxides(TixOy)and Al2TiO5(Al2O3·TiO2) were detected. After 850℃ 4 h annealing, it indicates that apart from the phases described above, Ti2Al and TiAl3 were formed. We suggest the chemical equations of reaction corresponding to the different temperature zones and discuss the limitation of the prediction from thermodynamic consideration by using bulk material data.