Abstract: The aim of this study was to investigate the thermal properties of D-Mannitol as a Phase Change Material (PCM) for latent heat storage system. Heat absorbed by D-Mannitol causes it to undergo a change from the solid to the liquid phase and this heat is stored as the latent heat of fusion. The stored energy can then be retrieved at a later time for various applications. The melting point and enthalpy of the fusion of D-Mannitol are important properties and these were determined by Differential Scanning Calorimetry (DSC) measurements. Melting was found to begin at 162.15°C and attained a peak at 167.8°C while the enthalpy of fusion was found to be 326.8 J g-1 for 10°C min-1. Furthermore the change in melting temperature and enthalpy of fusion for different heating rates were studied experimentally by DSC. D-Mannitol’s thermal stability was studied using the TG-DTG (thermogravimetry-derivative thermogravimetry) and TG-DTA (thermogravimetry-differential thermal analysis) curves. The TG-DTG curves revealed that thermal decomposition began at 300.15°C. The DTA curve had a sharp endothermic peak at 169.2°C followed by a broad exothermic one at 297°C. The curves showed that D-Mannitol decomposes in one prominent mass loss stage. The measurement of latent heat (enthalpy of fusion), melting point and decomposition point showed that D-Mannitol with a latent heat 326.8 kJ kg-1 and melting temperature 167.8°C is the most suitable PCM candidate for medium temperature applications because of a large temperature difference of 132°C between its melting point and decomposition temperature.