The isothermal oxidation process in bulk and powdered Ni2AlTi (L21 structure) has been studied in the temperature range of 600 to 1200° C in air by means of X-ray diffraction and scanning electron microscopy. At 900 and 1200° C, the transient oxides, NiO and TiO2 were formed in the initial stage on the outer surface. Subsequent oxidation was dominated by outward diffusion of aluminium, resulting in the formation of a Ni3Ti layer beneath an internal precipitation layer containing Al2O3-NiAl2O4 aggregates, NiTiO3 and Ni3Ti. Formation of NiTiO3 and NiAl2O4 at the expense of NiO, TiO2 and Al2O3 indicated the reaction among constituent oxides also occurred in the late stage of oxidation at 900 and 1200° C. Only NiO and TiO2 were identified in specimens oxidized at 600° C up to 24h. The oxidation rate of Ni2AlTi is of the same order of magnitude as the dilute γ-NiAl alloy at 1200° C.