The thermal energy storage performance and phase change stability of mix phase change materials consisted of stearic acid and Na2PO4 center dot 12H(2)O are studied by means of Fourier transformation infrared spectrum analyses (FTIR) and Differential Scanning Calorimetry (DSC). The specific heat capacity of mix materials is also determined experimentally. The results show that all absorption peaks of functional groups and chemical bonds of stearic acid still exist, which suggests that these crystal materials composed of stearic acid and Na2PO4 center dot 12H(2)O have good phase change stability and chemical compatibility. Thus, disadvantages caused by the subcooling of Na2PO4 center dot 12H(2)O and the low specific heat capacity of stearic acid can be solved, it is speculated that complement each other on the basis of organic/inorganic characteristics in itself is carried out for these two component materials of the mixture. (C) 2010 Elsevier Ltd. All rights reserved.