The K2SO4-Na2SO4 system was studied by differential scanning calorimetry (DSC) with the aim of developing a new phase-change thermal energy storage material. The temperature range of phase change is from 800°C to 1069°C according to the phase diagram. A new shape-stabilized phase-change material made of molten salts impregnated by capillary forces in a porous-fiber matrix was presented. These materials were characterized by X-ray diffraction analysis and differential scanning calorimetry analysis. The results indicated that the compound included 70~80% of molten salts, meanwhile the heat storage material could keep its shape without any leakage during the heating process.