The oxidation kinetics of hot-pressed Mo(Al0.01Si0.99)(2) and Mo(Al0.1Si0.9), were measured at 480degreesC, and between 1200degrees and 1600degreesC. The qualitative oxidation of arc-melted Mo(Al0.1Si0.9)(2), Mo(Al0.3Si0.7)(2), Mo(Al0.5Si0.5)(2), and Mo3Al8 was examined after 600degreesC for 1000 h in air. At all temperatures, the compositional difference between the materials yielded very different oxidation rates and scale microstructures. At 1400degrees and 1500degreesC, microstructural evolution of the oxide scales resulted in improved oxidation resistance at long times (>400 h). At these temperatures, a significant reduction in the long-time oxidation kinetics was correlated with the in situ formation of an inner mullite scale. At 480degrees and 600degreesC, oxidation resistance improved significantly with increasing aluminum concentration. Contrary to the behavior of MoSi2, samples of Mo(Al0.01Si0.99)(2) did not demonstrate catastrophic oxidation, and samples of Mo(Al0.1Si0.9)(2) were very oxidation resistant.