The dissolved hydrogen concentration in the water phase represents a key factor for corrosion characteristic of zirconium alloy. A zirconium alloy was oxidized for 100 d at two different concentrations, 2.49 and 4.15 mg/kg. In situ Raman peaks of the specific oxide phases changed, indicating the occurrence of phase transformation. Moreover, the result of transmission electron microscopy was compared with in situ analysis of the oxide structure formed on the zirconium alloy. The phase stability of the oxide could be influenced by the dissolved hydrogen, and it the phase transformation from tetragonal to monoclinic is influenced by dissolved hydrogen.