The solid-liquid phase transitions in lauric acid, palmitic acid. stearic acid and their binary systems have been studied by differential scanning calorimetry (DSC) and infrared spectroscopy at various temperatures. The temperatures of the solid-liquid phase transitions in binary systems are 32.84 +/-0.71 degreesC with DeltaH values of 146.5-195.1 J g(-1). The spectra shifts in the temperature range corresponding to the solid-liquid phase transition showed that the solid-liquid phase transition of fatty acids is related to intermolecular hydrogen bonds.