A novel approach has been explored to prepare brain-like polyaniline (PANI) nanostructures with many convolutions (140-170 nm in average diameter) using aniline/citric acid (CA) salt as the template and chlorine gas as the oxidant by a gas/solid reaction for the first time. The method provided here differs significantly from the traditional one in which the polymerization of PANI is usually carried out in acidic solution.