Nanofibers of AlOOH with controllable aspect ratios have been synthesized by a facile steam-assisted solid-phase crystallization route. The morphology and aspect ratios of resulting AlOOH nanofibers were significantly influenced by the alkaline medium used in the preparation of solid precipitates from Al(NO3)3 solution. When tetramethylammonium hydroxide was used for precipitation, straight rod-like nanofibers with aspect ratios of 10-20 were obtained. The use of other tetra-alkylated ammonium hydroxides, such as tetraethylammonium hydroxide, tetrapropylammonium hydroxide or tetrabutylammonium hydroxide, led to the formation of long wire-like nanofibers with aspect ratios up to 150. After thermal treatment at 600°C, the morphologies of the one-dimensional nanostructures were well preserved while the crystal structure was converted to γ-alumina. The wire-like nanofibers of alumina possessed higher thermal stability than alumina nanorods, and both exhibited much higher stability as compared with alumina micropowder.