Two eutectic mixtures: stearic acid-n-butyramide and stearic acid-n-octanamide were studied as phase change materials. The eutectic mixtures featured low melting points and high latent heats of fusion for solar heat application. Solid-liquid phase diagrams for the two mixtures were developed. The melting temperatures and latent heats of fusion of eutectic composition were predicted by a modeling method.