Abstract: A photoacoustic piezoelectric method based on a simplified themoelastic theoretical model is employed to determine thermal diffusivities of solids and composites. Under the optimal experimental conditions, we study the effective thermal diffusivity of a composite (Al2O3x/SAE321) with short A12O3x fibers reinforced Al-alloy matrix (SAE321). The results show that this method is quite convenient and effective in measuring the thermal diffusivity of both solids and composites, especially for the measurement of those with micro-inhomogeneous structures.