We have investigated the thermal desorption properties and the temperature dependence of surface characteristic of a titanium alloy material using thermal desorption spectroscopy (TDS) and X-ray photoelectric spectroscopy (XPS). The results show drastic changes on the titanium oxide core XPS levels (TiO₂ : 2P_1/2, 2P_3/2) of the surface, i.e. the TiO₂ decomposed into the suboxides at 200°C, the suboxides vanish and metal Ti appears above 450°C. This sensitive change of the surface oxide layer affects to the hydrogen gas desorption of a titanium alloy, e.g. amount of the hydrogen gas desorption drastically increases with temperature above 450°C. This implies that the surface oxide layer acts as a barrier for the bulk hydrogen diffusion.