We have developed low-temperature thermal energy storage material using fatty acids. The fatty acids, capric and lauric acids, were used as solid-liquid phase change materials (PCMs) at temperatures between 0 and 7degreesC. The thermodynamic properries of PCMs were investigated in detail by utilizing a differential scanning calorimeter (DSC). We found that the solid-liquid phase change temperature was freely controllable by adjusting the mixture of the two-component system (capric and lauric acids). Furthermore, we researched the additive effect of unsaturated fatty acids (oleic acid, ricinoleic acid, or linoleic acid), anionic and nonionic surfactants (sodium di (2-ethylhexyl) sulfosuccinate, S 1 -4, T 1-4), and surfactants derived from a Paty acid (sodium oleate or sodium laurate). In particular, the addition of 20 wt% sodium oleate was effective to suppress the supercooling temperature and control the solid-liquid phase change temperature between 0 and 7degreesC. No physicochemical degradation of the capric and lauric acids with 20 wt% sodium oleate was found in the 50 recucling tests bymeans of the DSC analysis.