Anodization of aluminum in acidic electrolyte containing chloride ions was used to prepare aluminum ultrafine particles (Al UFPs) for the first time. In addition, the influence of different acid electrolyte was investigated and the mechanism of generating Al UFP's is analyzed. It is found that the pitting corrosion of chloride ions plays an important role in preparing Al UFPs and the acidification of the electrolyte is in favor of the preparation. Al UFPs with different shape and size distribution were obtained via changing the type of acid. Finally, the model of generating Al UFPs via this method is proposed. (C) 2008 Elsevier Ltd. All rights reserved.