Ultrafine fibers of polyethylene glycol/cellulose acetate (PEG/CA) composite in which PEG acts as a model phase change material (PCM) and CA acts as a matrix, were successfully prepared as thermo-regulating fibers via electrospinning. The morphology observation from the electrospun PEG/CA composite fibers revealed that the fibers were cylindrical and had a smooth external surface. PEG was found to be both distributed on the surface and within the core of the fibers. Differential scanning calorimeter (DSC) was used to characterize the thermal properties of the composite fibers. The results indicated that the fibers imparted balanced thermal storage and release properties for their thermo-regulating function and the thermal properties were reproducible after 100 heating-cooling cycles. (c) 2007 Elsevier Ltd. All rights reserved.