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The precipitated silicide phase in a high-Nb TiAl alloyed with Si addition was studied. Unlike the Ti 5 Si 3 precipitates formed in Ti–Al–Si ternary system, the silicide particles formed in this study consisted of a Nb 5 Si 3 (designated as ε) phase and had a hexagonal D8 8 crystal structure. The volume fraction of Nb 5 Si 3 phase increased after heat treatment at 1473 K for 30 min as the B2 phase decomposed. A large number of Nb 5 Si 3 precipitated on lamellar boundaries and had a specific orientation relationship (OR) with α 2 and γ:(1 1¯ 0 0) ε//(1 1¯ 0 0) α 2 and [1 1 2¯ 3] ε//[1 1 2¯ 0] α 2;(1 1¯ 0 0) ε//(1 1¯ 2¯) γ and [1 1 2¯ 3] ε//[1 1 0] γ. The semi-coherent interfaces of Nb 5 Si 3 with the matrix resulted in regular interface dislocations.