A series of diacid dioctadecyl esters (DADOEs) were synthesized as novel solid-liquid phase change materials (PCMs) by esterification of octadecanol and ethane diacid, butane diacid, adipic acid, octane diacid and sebacic acid and then, ultrafine phase change fibers of DADOE/polyethylene terephthalate (PET) were fabricated via electrospinning as form stable PCMs. It is found that the DADOE/PET composite fibers have good morphology with smooth surface when DADOE content is lower than 50% (w/w, with respect to PET matrix), and the average fiber diameter increases gradually with the increase of DADOE content from 375 nm (pure PET fibers) to more than 1 mu m. The fiber morphology has no obvious variation after thermal cycles, which confirms that DADOE/PET fibers have the characteristic of form stable phase change. The results from DSC curves show that DADOE/PET fibers impart reversible phase change behaviors similar to those of DADOEs, and the enthalpies of the composite fibers increase with the increase of DADOE content (the highest enthalpy of melting for the fibers is more than 65 J/g). In addition, the thermal performances of the composite fibers could be well maintained after thermal cycles, which indicates that the fibers have good thermal stability and reliability. (C) 2011 Elsevier B.V. All rights reserved.