Monodisperse porous α-Fe₂O₃ ellipsoids composed of primary nanocrystals were synthesized by a facile one-step template-free hydrothermal method. Field emission scanning electron microscopic and transmission electron microscopic results revealed that these porous ellipsoids were built from a large number of nanoparticles with sizes of about 10–20 nm. The morphology and size of the as-prepared products could be tailored by simply adjusting the amounts of hexamethylenetetramine and reaction temperature. A possible formation mechanism was proposed on the basis of the results of time-dependent experiments. When used as sensing materials in chemical sensors, the as-prepared porous α-Fe₂O₃ ellipsoids exhibit a high response to ethanol.