Oxidation behavior of Ti-45at%Al-1.6at%Mn intermetallic compounds fabricated by respectively a reactive sintering and a melt process was studied at the temperature range of 800 1100℃. The reactive-sintered alloy showed superior oxidation resistance to the melted alloy above 900℃. Protective Al₂O₃ scale was formed up to 1000℃ on the reactive sintered alloy, while such scale was only visible at 800℃ for the melted alloy. According to Pt diffusion marker experiment it was found that oxide scale of the reactivesintered alloy grows inward below 1000℃, while both the inward and outward growth of oxide scale is observed for the case of the melted alloy above 900℃. The excellent oxidation resistance of the reactive-sintered alloy was considered to be due to the existence of chlorine, and/or both carbon and chlorine which were introduced from raw titanium powders. Chlorine could decrease oxygen ion vacancies in TiO₂ from the early stage of oxidation so that TiO₂ growth was interrupted and protective Al₂O₃ scale was easily formed on the reactive-sintered alloy. The growth of TiO₂ could also be interrupted by the chlorination of TiO₂ at the presence of both Cl₂ and C, or both Cl₂ and CO for the reactive-sintered alloy.