The thermal expansion behaviors of SiC whisker reinforced pure aluminum composite cooled down from 580degreesC with lower and higher cooling rates were studied in the present research. The results indicated that the thermal expansion behaviors of the composite were affected by the cooling rate greatly. The results of transmission electron microscope observation and X-ray diffraction analysis indicated that the dislocation density and thermal mismatch stress (TMS) in slowly cooled composite were lower than those in fast cooled (water quenched) composite. The analysis suggested that the coefficient of thermal expansion (CTE) was closely related to the change rate of TNIS and the dislocation density of matrix of the composite. The changing tendencies of TMS in composites with different microstructures and TMSes on heating were also analyzed. (C) 2002 Published by Elsevier Science B.V.