NbSi2 is a promising candidate as a coating material for Nb-base alloys. However, it shows complicated oxidation behavior, depending on oxidation temperature. In the present study, in order to clarify the oxidation resistance of NbSi2, oxidation tests of sintered NbSi2 were carried out at temperatures ranging from 773 to 1673 K in air. Moreover, the effect of addition of boron on oxidation resistance of NbSi2 was clarified. NbSi2 showed accelerated oxidation at temperatures of 1073 K and above. The accelerated oxidation was caused by formation of a porous oxide layer, which may be due to the phase transformation from amorphous to crystalline SiO2. The addition of boron to NbSi2 leads to the formation of a protective borosilicate layer, resulting in great improvement of the oxidation resistance. Consequently, NbSi2 added with boron shows excellent oxidation resistance up to at least 1673 K
