The utilization of phase change materials (PCMs) exhibiting exceptional thermal properties holds great significance for the advancement of sustainable energy utilization systems. Consequently, this research delves into the exploration of an innovative composite PCM formulated from a blend of stearic acid-adipic acid (SA-ADA) and expanded graphite (EG), with the SA-ADA component constituting 91 % of the total mass. Through rigorous analysis, the microstructural, chemical and crystallographic characteristics of the composite were confirmed, revealing a uniform distribution of SA-ADA within the porous EG matrix, indicative of their exceptional compatibility without any discernible chemical interaction. Notably, the SA-ADA/EG composite exhibited a melting point of 65.7 °C and a latent heat of 185.3 kJ/kg, indicating its remarkable thermal performance. Furthermore, the thermal conductivity of this composite was significantly enhanced, achieving 8.375 W·m−1·K−1, which represents a remarkable 27.7-fold improvement over that of pure SA-ADA. This enhancement translated into substantial reductions in charging and discharging durations by 65.7% and 32.7%, respectively. Thermogravimetric analysis revealed that the thermal decomposition threshold far exceeded the phase change temperature, demonstrating robust thermal stability of the composite. Additionally, after enduring 500 thermal cycles, the composite demonstrated exceptional cycling stability. These findings suggest the great potential of SA-ADA/EG composite PCMs as promising candidates for thermal storage applications.