Fe3Al nanoparticles have been synthesized by the hydrogen plasma-metal reaction method. In order to study the oxidation behaviour of the intermetallic nanoparticles, changes in morphology, particle size and crystal structure during heat treatment in air were investigated by transmission electron microscopy and x-ray diffraction. The as-prepared nanoparticles were stable both in shape and structure at 473 K where the iron nanoparticles were known to be oxidized fully. The high oxidation resistance of intermetallic nanoparticles was attributed to the aluminum oxide layer. The oxidation of Fe3Al nanoparticles proceeded slowly below 573 K and rapidly above this temperature. The oxides formed between 473 and 673 K were Al2O3 and a mixture of iron oxides (alpha-Fe2O3 and gamma-Fe2O3) changing into single phase alpha-Fe2O3 at 873 K. The nanoparticles started to grow by coalescence at 573 K and the mean particle size was larger than 100 nm above 673 K.