The analysis of the oxidation of MoSi2 at room temperature was carried out using X-ray photoelectron spectroscopy. A clean surface of MoSi2( )was obtained by sputter-etching the bulk material inside the spectrometer, and the chemical states of the surface were examined with both high and low take-off angles for the conditions of as-etched and exposed to the air for different times, The commercially pure MoSi2 powder was also investigated in the as-received condition. The analysis indicated that the exposure of a clean molybdenum disilicide to the air for just a few minutes led to the formation of SiO2 and MoO2, and this oxidation would persist at least for more than 24 h with the final surface of MoSi2 being covered by a duplex oxide layer of SiO2 + MoO3.