Abstract: A series of TiAl+Nb alloys with various Nb contents has been employed to explore phase relationship and the evolution of microstructure.A new ordered γ derivative (γ₁) has been observed in the alloy containing 20 at% Nb.The additional diffraction spots added to the diffraction pattern of L1₀ (TiAl) structure have been found in the alloy containing Nb up to 11 at% in terms of further ordering.The transformation from L1₀ (TiAl) structure to the further ordering phase,γ₁,is a continuous ordering process with the substitution of Nb atoms for Ti atoms in alloys with over-stoichiometric Al content of TiAl.The possible transformtion characterzation has been discussed.