Single-crystal aluminum borate (Al4B2O9) nanowhiskers with diameters from 20 to 200 nm have been synthesized on the surface of aluminum powder at relatively low temperatures after high energy ball-milling pretreatment. It was found that the reaction temperature plays an important role in determining the diameter and length of the single-crystal Al4B2O9 nanowhiskers. The growth of the nanowhiskers can occur at a low temperature of 650 degrees C due to the ball-milling pretreatment. The growth mechanism of the nanowhiskers is considered to be the solution-liquid-solid (SLS) growth. Our in-situ growth of nanowhiskers on the aluminum matrix is an effective way to prepare Al4B2O9 nanowhisker/aluminum composite powders with homogenous distribution of the reinforcement. (C) 2011 Elsevier B.V. All rights reserved.