To develop new organic PCMs for use in hot water supply, an attempt was made to adjust the melting temperature as well as the latent heat, by adding polyalcohol to erythritol, which has a melting temperature of 119 degrees C and a latent heat of 340 kJ/kg. The present study employed seven different polyalcohols: trimethylolethane, trimethylolpropane, 2-ethyl-2-methyl-1,3-propanediol, pinacol, dithioerythritol, xylitol and sorbitol. Thermophysical properties of latent heat and melting temperature of the binary mixtures of erythritol and polyalcohol were measured by means of a DSC. The data on the melting temperature and the latent heat were compared with those obtained by ideal enthalpy change in fusion of a binary mixture and thermodynamic equilibrium equation between a liquid and solid phase, respectively. As a result, the latent heat of erythritol-polyalcohol mixtures could be estimated by the sum of latent heat of each component within a mean square error of 13%, in accordance with the weight ratio of erythritol and polyalcohol. Further, the melting temperature of a new organic PCM could be predicted within an error of 7% by an expression for the ideal solubility of a solid solute in a liquid solvent that takes into account the activity coefficient of the solution.