As the starting material of molybdenum manufactured by powder metallurgy, molybdenum powder is used. To investigate the elution in water of the molybdenum powder used as a raw material, the molybdenum elution was analyzed by ion chromatography and X-ray photoelectron spectroscopy (XPS). It was clarified that the elution based on MoO42- takes place as determined by ion chromatography. Results of the surface measurement by XPS revealed that, the molybdenum oxidized in air on the surface exists mainly as molybdenum (VI) oxide (MoO3), which is the most stable oxide. The molybdenum (VI) oxide elutes promptly in water compared with the metal powder. The oxide on the molybdenum metal surface, which was assumed to be eluted promptly, became thin, and the elution was repeated again by oxidation in water through molybdenum (IV) (MoO2), (V) (Mo2O5) and (VI) oxides, and the solution was clarified to elute through molybdenum (VI) oxide.