Sintering is generally recognized as a consolidation process of the powder compacts. However, the swelling problem is always observed in a stress-free reactive sintering of iron-aluminum elemental powder mixtures. Present study on the stress-free vacuum sintering of Fe-29 at.% Al (for sintered Fe3Al) compacts indicated that the transitory appearance of an intermediate phase, Fe2Al5, attributed to this swelling behavior. Further study on the Fe-71.5 at.% Al (for sintered Fe2Al5) compacts shows that a large and rapid increase of the specimen's dimension occurred during a low temperature sintering process, meantime, a sponge-like porous microstructure was obtained. An in situ temperature variation was monitored on these Fe-Al compacts, and a violent and rapidly exothermic heat was found. Compared with the thermal behavior of Ni-Al compacts, it is suggested that many simultaneous fast reactions have occurred inside the Fe-Al mixture during sintering and cause the swelling phenomenon. (C) 2004 Elsevier B.V. All rights reserved.