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Three types of Ti-Al-Nb ternary alloys were prepared by arc-melting and heat treatment, i.e. γ-TiAl single phase alloy (alloy A), γ-TiAl + α2-Ti3Al duplex phase alloy (alloy B) and γ-TiAl + α2-Ti3Al + Nb2Al multiple phase alloy (alloy C). The phase stability was studied using SEM, XRD and electron probe microanalyzer. Mechanical properties were investigated through tensile tests at room temperature and 1173 K. Results show that their tensile properties are closely related to their microstructures. The deformability of alloy B is better than that of alloy A and C at room temperature due to small grain size caused by α2 phase appearance, lamellar microstructure of (γ+α2) and tremendous γ/α2 interface. The deformability of alloy B increases significantly with increasing temperature and its elongation achieves 40.4% at 1173 K. The fracture mode of alloy B changes from brittle transgranular failure at room temperature to ductile failure at 1173 K. While, both of alloys A and C have no increased deformability at 1173 K and show brittle transgranular failure at the two temperatures. Alloy C is a kind of very brittle material at room and elevated temperature, due to Nb2Al phase appearance reducing the continues degree of (γ+α2) lamellar structure.