Abstract: The eutectic point of the molecular alloy of capric acid and stearic acid was calculated by Schroeder equation. A series of binary systems of capric acid and stearic acid with various proportions were prepared by melt stirring method on the basis of eutectic point calculation. DSC, gradual cooling and melting tests, thermal conductivity test, TG and accelerated thermal cycle test were employed to analyze their thermal properties and thermal reliability, and to draw the phase diagrams of the binary systems. The results show that capric acid and stearic acid have no distinct eutectic temperature but a completely miscible range. The eutectic systems with mass ratios of capric acid of 85% and 90% have low melting temperatures of 30.5 ℃ and 30.8 ℃, with their latent heat of fusion values of 155.5 J/g and 161.0 J/g, respectively. After 1 000 thermal cycles, the phase change temperature and latent heat of the eutectic system with 90% capric acid change a little.