Syntheses of boehmite particles were performed by precipitation of aluminium nitrates with soda in conditions of controlled pH and temperature. If precipitation conditions lead first to an isolable amorphous hydroxide subsequently transformed into boehmite, then porous particles constituted by the agglomeration of boehmite nanocrystals are formed. In contrast, if conditions directly lead to a crystallized boehmite phase, polycrystalline nanofibers are obtained. These experiments show that anisotropic growth can be obtained by monitoring pH and temperature, without using any additives.