The thermal expansion behaviors of an aluminum matrix composite reinforced with aluminum borate whiskers and Fe3O4 particles were studied. The results indicated that the coefficient of thermal expansion (CTE) of this kind of composite was lower than that of the aluminum matrix composite reinforced with aluminum borate whisker. The CTE of the as-cast composite decreased with the increasing content of Fe3O4 Particles. It was also found that there was a minimum of CTE in the temperature range from 200 to 400 degrees C for an as-cast composite with a higher volume fraction of Fe3O4 particles. However, after one thermal cycle between 30 and 450 degrees C, the minimum of CTE disappeared and the CTE of the composite became stable in the same temperature range. The results indicated that the abnormal thermal expansion behavior was resulted from the reduction of the partial oxidized Fe3O4 in the composite during the heating process. (c) 2005 Elsevier B.V. All rights reserved.