The oxidation and the simultaneous oxidation and sulfidation of Ti-6Al-4V and SP-700 were studied in air and in H2/H2O/H2S gas mixture over the temperature range 700~1000 ℃. The results indicated that the oxidation and the simultaneous corrosion kinetics followed the parabolic rate law at all temperatures. In general, the corrosion rates of both alloys are faster than their oxidation rates. The scales formed on Ti-6Al-4V and SP-700 after oxidation were composed of TiO2 and α-Al2O3, while the scales formed in H2/H2O/H2S gas mixture consisted of mostly TiO2 and minor Ti(subscript 1-x)S. The formation of Al2O3 is responsible for the reduction in oxidation rates for the two alloys as compared to their corrosion rates.