The invention relates to a method for preparing a carbon aerogel from agglomerated carbon nanotubes, that comprises the following steps: (A) preparing an aqueous dispersion of carbon nanotubes in water in the presence of a dispersing agent; (B) forming a foam from the nanotubes aqueous dispersion of step (A) by bulking under the action of a gas in the presence of a foaming agent; and (C) freezing the foam obtained in step (B) and removing the water by sublimation. The invention also relates to the carbon aerogels thus obtained, and to their use essentially as partition materials or biomaterials.