The effects of chlorine on the high temperature (900-1115 o C) oxidation resistance of γ-TiAl-based alloys were studied by applying MnCl 2 on the sample surfaces of the Ti47Al, Ti55Al, Ti47Al3V and Ti47Al2Cr2Nb alloys. The oxidation rates of these alloys decreased remarkably after treating the sample surfaces with MnCl 2 . The oxide scales formed on TiAl based alloys generally consisted of a TiO 2 -rich outer layer and a TiO 2 +Al 2 O 3 mixed inner layer. After surface treatment with MnCl 2 , a very convoluted scale consisting of a thin discontinuous TiO 2 outer layer and continuous Al 2 O 3 inner layer with a small amount of TiO 2 formed on the four alloys. At the initial stage of oxidation the continuous Al 2 O 3 layer had formed on the MnCl 2 treated samples. It is suggested that occurrence of chlorination of aluminium during the initial stage promoted the formation of the continuous Al 2 O 3 layer.