Active carbon is used as an absorbent material because of its porous structure. Stearic acid/active carbon composite phase-change materials were synthesized by physical absorption with stearic acid as the phase-change material and active carbon as the carrier to maintain a stable shape. Thermogravimetric analysis, differential scanning calorimetry, a physical property measurement system, and Fourier transform infrared spectroscopy were used to determine the thermal stability, phase-change temperatures and enthalpies, thermal conductivities, and structures of the samples, respectively. The samples were found to have good thermal stability. The stearic acid and active carbon in the synthesized materials were simply physically combined. The maximum absorption ratio of stearic acid in the samples was 79.48 wt %; the melting and solidifying temperatures were 52.83 and 51.74°C, respectively; and the melting and solidifying enthalpies were 108.2 and , respectively. The thermal conductivities of the samples were enhanced by active carbon.