As a novel solid-liquid phase change in material (PCM), stearyl stearate (SS) was synthesized by esterification of stearyl alcohol and stearic acid, and the ultrafine composite fibers of SS/polyethylene terephthalate (PET)were prepared via electrospinning as form stable PCMs. The structure of SS, morphology and thermal properties of SS/PET composite fibers were characterized by FI-IR, FE-SEM and DSC, respectively. The average diameter of SS/PET composite fibers measured from the SEM images increased gradually with the increase of SS percentage, and the morphology of the composite fibers had no obvious variation after thermal treated. which confirmed the developed material had the feature of form stable phase change. The results from DSC showed that the enthalpy of the composite fibers increased with the increase of SS content, but the variation of SS percentage in the composite fibers had few influence on phase transition temperature of the fibers. In addition, the thermal performances of the fibers could well be maintained after 100 heating-cooling thermal cycles, which indicated that the composite fibers had good thermal stability and reliability. (C) 2009 Elsevier B.V. All rights reserved.