The thermal expansion behaviour of Duralcan composites having a matrix of hypoeutectic AI-Si alloy containing SiC reinforcements ranging from 10-40 vol% was investigated. The coefficient of thermal expansion (CTE) of the MMCs was measured between 25 and 350 degrees C by a high-precision thermomechanical analyser, and compared to the predictions of three theoretical models. At low temperature, the experimental CTEs show substantial deviation from the predictions of the elastic analysis derived by Schapery, while the Kerner model agrees relatively well at high temperature. The overall measured CTE, in the range of 25-350 degrees C, as a function of the volume fraction of SiC is well predicted using Schapery＇s lower bound. We interpret these features as being an effect of reinforcement phase geometry and the modified microstructure derived from the Duralcan process and subsequent heat treatments.