In-situ heating transmission electron microscopy (TEM) was employed to investigate the initial stage of lamellae formation in a high Nb containing γ-TiAl based alloy. A Ti-45Al-7.5Nb alloy (at %), which was heat treated and quenched in a non-equilibrium state such that the matrix consists of ordered α2 grains, was annealed inside a TEM up to 750 °C. The in-situ TEM study reveals that γ laths precipitate in the α2 matrix at ∼750 °C possessing the classical Blackburn orientation relationship, i.e. (0001)α2 // (111)γ and [11-20]α2 // <110]γ. The microstructure of the in-situ TEM experiment is compared to results from ex-situ heating and subsequent TEM studies.