To improve the energy storage efficiency of phase change composites, porous mullite was used to encapsulate the PCM-palmitic acid and graphite powder was applied to enhance the overall thermal conductivity. During the experimental process, a series of palmitic acid/mullite/graphite (PA/mullite/GP) composites were prepared to obtain the PA/mullite/GP form stable phase change material (FSPCM) by facile direct impregnation method. Then their microstructure, chemical compatibility and thermophysical properties were studied by the method of SEM, FTIR, XRD, DSC, TGA and PR, systematically. The DSC results demonstrate that the PA, PA/mullite and PA/mullite/GP have the enthalpy of melting of 213.J/g, 54.7 J/g, and 52.J/g, while the enthalpy of freezing of 217.0J/g, 53.6J/g and 51.5J/g, respectively. Compared with the pure PA, the thermal conductivity of the prepared PA/mullite/GP has been improved from 0.28 W m(-1) K-1 to 0.52 W m(-1) K-1 owing to the high thermal conductivity of GP (only 5 wt %). The reliability test shows that the PA/mullite/GP FSPCM maintains form-stable without any PA leakage even after 150 thermal cycles. In short, prepared PA/mullite/GP FSPCM exerts excellent chemical and thermal reliability and thus has a bright prospect in the field of solar energy storage and solar heating. (C) 2019 Published by Elsevier Ltd.