Abstract: Thermal stability of some phase change materials(PCMs) of fatty acids including capric,lauric,myristic and palmitic acid with melting temperature between 30~65℃ were studied.The melting temperature and fusion latent heat of the acids were determined by using DSC technique after 56,112,200 and 400 times thermal cycles.The accelerated thermal cycle tests indicate that the melting temperature and fusion latent heat of the acids change slightly and irregularly with thermal cycles and the acids as latent heat energe storage materials have a thermal stability good enough for the expected thermal cycles of one year use.