A new composite phase change material was fabricated by adding 0.05, 0.1, 0.15, and 0.2 wt.% CuO nanoparticles into lauric acid, separately. The SEM was used to observe the morphological structures of as-prepared nanoparticles, and X-ray diffraction analysis was used to characterize their crystalline structure. The phase change properties (phase change temperatures and latent heats) of lauric acid and composite phase change materials were obtained using differential scanning calorimetry. Using a laser flash analyzer, the thermal conductivity enhancement of the composite phase change materials was evaluated. The thermal reliability analysis was implemented to ascertain the results of the composite phase change materials over long periods.