NbSi(2) 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 NbSi(2), oxidation tests of sintered NbSi(2) were carried out at temperatures ranging from 773 to 1673 K in air. Moreover, the effect of addition of boron on oxidation resistance of NbSi(2) was clarified. NbSi(2) 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 SiO(2). The addition of boron to NbSi(2) leads to the formation of a protective borosilicate layer, resulting in great improvement of the oxidation resistance. Consequently, NbSi(2) added with boron shows excellent oxidation resistance up to at least 1673 K.