Differential scanning calorimetry (DSC) was used to study the kinetics of S' and theta' precipitation in AA2618 and its composite containing 15 vol % Al2O3 particles. The unreinforced alloy and the composite were fabricated by a proprietary casting method, followed by extrusion. The DSC studies were carried out on as-quenched samples of the test materials. The precipitation of the S' and theta' phases in both materials was found to be kinetically controlled and obey the modified Avrami-Johnson-Mehl equation. The growth mechanisms for S' and theta' formation in AA2618 seemed unaffected by the addition of Al2O3 particles. The growth parameters obtained for the precipitation of these phases in the matrix alloy and the composite were not significantly different.