The influence of the NbAl3 microstructure on its oxidation mechanism was investigated in air under atmospheric pressure over the temperature range 500-1080 degreesC. Different processing techniques as induction melting and mechanically-activated annealing processes (M2AP) were used to produce the intermetallic compound NbAl3. A protective external alumina scale grew only on Al-enriched NbAl3 between 700 and 1080 degreesC. Stoichiometric NbAl3 exhibited the "pesting" phenomenon between 550-900 degreesC, whereas a non protective lamellar oxide scale formed above 900 degreesC. The proposed oxidation mechanism explains these observations which are in agreement with the oxidation study of powders with different crystallite sizes.