In this paper, a phase-change-material/lightweight aggregate (PCM-LWA) composite thermal energy storage material was prepared by absorbing the lauryl alcohol, which is one kind of phase change materials, into porous lightweight aggregates (LWAs) that have an excellent absorbability. In such a composite, the lauryl alcohol serves as a latent heat storage material and the porous lightweight aggregate acts as the supporting material. In order to prevent the melted lauryl alcohol leak from the porous LWAs, surface seal processing for the PCM-LWA was necessary. In this research, pure cement paste and polymer modified cement paste were used to seal the PCM-LWA surface. Through comparison between the differential scanning calorimetry (DSC) tests for lauryl alcohol and PCM-LWA, it can be known that the solid-liquid phase change temperature of the composite PCM-LWA was slightly higher than that of the lauryl alcohol, and latent heat of the PCM-LWA was smaller than that of the pure PCM.