Abstract PEG based thermosetting phase change materials (PCMs) have been frequently employed for thermal energy storage in building and other fields due to the low cost, no toxic, no corrosive, good thermal properties and no leakage in phase change process. In this article, thermosetting PCMs with polyethylene glycol (PEG) as phase change functional chain and polyaryl polymethylene isocyanate terminated polycarbonatediol (PCD) as curing agent were prepared through a facile and solvent-free bulk polyaddition. This preparation strategy can provide novel mean to design and synthesize PEG based thermosetting PCMs with different structure and performances according to the specific requirement. Moreover, the introduction of PCD will further improve the performance of PCMs. The chemical structure, crystalline properties, phase change properties, thermal reliability and stability of prepared PCMs were investigated by Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), polarizing optical microscopy (POM), differential scanning calorimetry (DSC), accelerated thermal cycling testing and thermogravimetric analysis (TGA), respectively. FTIR spectra showed that the PEG based thermosetting PCMs were successfully synthesized. XRD and POM results indicated the similar spherulite structure of virgin PEG and prepared PCMs, and the crystallinity and crystal size of PCMs are affected by the introduction of curing agent. Meanwhile, DSC measurements showed that prepared PCMs have good phase change properties. Accelerated thermal cycling and TGA testing proved the excellent thermal reliability and thermal stability of prepared PCMs.