The ultrafine phase change fibers (PCFs) with core-sheath structure based on polyethylene glycol/cellulose acetate (PEG/CA) blends were fabricated successfully via coaxial electrospinning for thermal energy storage. SEM and TEM images show that cylindrical and smooth phase change fibers are obtained and PEG as a phase change ingredient is encapsulated completely by CA sheath. The morphology of the composite fibers before and after thermal treatment indicates that the prepared fibers are form stable phase change materials (PCMs). The results from DSC demonstrate that the composite fibers impart balanced and reversible phase change behaviors, and phase transition enthalpies of the composite fibers increase with the increasing of PEG content in the fibers, while the phase transition temperatures of the fibers are similar with those of pure PEG. The stress-strain curves show that the ultimate strength and ultimate strain of the composite fibers are lower than those of CA fibers, and they decrease with the increase of PEG content. The PEG/CA composite fibers have extensive applications as a smart material for thermal energy storage and temperature regulation. (C) 2013 Elsevier Ltd. All rights reserved.