Abstract: The reduction of LaCoO_3 has been studied by XPS. It is shown that the degree of reduction of cobalt is characterized by the peak intensity of shake-up satellite of Co 2p_(1/2) level. The reduction of Co~(3+) to Co~(2+) in LaCoO_3 is appeared at 400 ℃. When LaCoO_3 is reduced by H_2 at 600 ℃, the cobalt is converted into metallic form, meanwhile the structure of La_2O_3 is identified by X-ray diffraction. After reduction of LaCoO_3 the separation energy between La 3d_(5/2) level and its shake-up satellite peak is 3.1 eV and the intensity ratio of shake-up satellite to its parent peak for La 3d_(5/2) level is 0.76. These values are approximately sam e as those of La(OH)_3, but they are different from those of La_2O_3. Therefore, La(OH)_3 is formed on surface after reduction of LaCoO_3.