Following aluminum pack cementation on Mo-Si-B alloys, the oxidation response has been examined in the range 700-1400 degrees C in 0.20x10(5) Pa of oxygen under isothermal and cyclic conditions. The initial coating is mainly composed of Mo3Al8, which reacts with the oxygen to produce a surface layer of alumina. The alumina slows the rate of oxidation considerably. The coating also reacts with the alloy substrate to develop an intermediate layer mainly composed of Mo-3(Al,Si) A15 phase. The kinetics of the oxidation and intermediate A15 phase formation reactions have been evaluated in order to model the alloy substrate recession and the overall coating lifetime.