The influence of aluminum, tungsten, and chromium alloying additions to MoSi2 on scale formation during high-temperature oxidation was studied. For the study MoAl0.7Si1.3 alloys were chosen with a maximum content of Al in C40 phase which was obtained. The surface of aluminum-alloyed MoSi2 is sealed with a dense alumina scale as a result of preferential oxidation of aluminum. Partial substitution of W for Mo in aluminum-alloyed MoSi2 does not significantly change the mechanism of alumina scale formation during oxidation. In the case of Cr substitution for Mo, the scale contains alumina as well, but some dissolution of Cr in alumina is present. The influence of alloy porosity on the oxidation rate of aluminum-alloyed MoSi2 was studied. The scale formed on porous samples was found to consist of a glassy oxide with considerable amounts of SiO2, which lends to a relatively high oxidation rate.