In this research, the effects of activated carbon from corncob (ACC) biomass as the supporting material were investigated on leakage problem and thermal properties of palmitic acid (PA) as a phase change material (PCM) for thermal energy storage, using the impregnation method. The leakage test demonstrated that the addition of ACC significantly reduced the leakage of PA. Furthermore, it was evident from ATR-FTIR spectra and XRD results that PA and ACC did not undergo any chemical reactions, and the crystal structure of PA was not changed, while the ACC was amorphous. According to the SEM result, ACC had a porous structure, and its increase in PA caused a larger pore volume and a higher specific surface area, which could prevent the leakage of PA. The thermal stability of the composites was measured by TGA. The results revealed that the addition of ACC slightly accelerated the pyrolysis of PA, improved the thermal conductivity of PA, and had enough thermal stability below 150 °C to be suitable for building and solar thermal energy storage applications. DSC analysis of the form-stable PCM showed a melting temperature of 61.25 °C and a melting latent heat of 81.57 J g −1 , and demonstrated high thermal reliability after 10 cycles, indicating excellent energy storage capacity. The BET test revealed that the ACC with 1364.70 m2 g −1 have a great potential to use for supporting material, and the composites were mesoporous, which prevented the leakage of PA.