The thermo-physical properties of the phase-change latent heat storage material fatty acid were elucidated in order to examine its temperature dependency. Heat transfer by natural convection was also investigated in a horizontal enclosed rectangular container filled with fatty acid, which was heated at the lower surface and cooled at the upper surface. he heat transfer coefficient of the liquid phase was found to coincide well with the conventional heat-transfer correlation of natural convection heat transfer in a horizontal enclosed rectangular container by applying the values of thermo-physical properties obtained in the present work.