In recent years, the gap of energy demand among seasons or between daytime and nighttime in Japan are steadily expanding, and technological development concerning effective use of energy is an urgent issue coupled with recent environmental problems. We focus on fatty acids (capric acid, lauric acid and myristic acid) and their mixture having unique phase change characteristics as a working fluid for a heat exchange system with multistage latent heat storage. These fatty acids as heat storage materials are easy to handle and less influenced on human body near ambient conditions. When the fatty acids mixed with a suitable mixing ratio are in the liquid phase state, the thermophysical properties (density, viscosity, melting and freezing points, supercooling character, effects of mixing ratio and so on) were identified in order to establish a new heat exchange system with multistage latent heat storage. As a result, thermophysical properties of the fatty acids and their mixture were evaluated quantitatively and were newly proposed as an appropriate heat transfer database.