A series of hyperbranched polyurethane (HB-PU) phase change induced energy storage materials were prepared by polyethylene glycol (PEG), methylene diphenyl 4,4'-diisocyanate (MDI), and hyperbranched polyester polyalcohol via a two-step process. The influence of thermal characteristics of HB-PU was investigated using differential scanning calorimetry (DSC) and wide-angle X-ray diffraction (WAXD). It has been found that the thermal characteristics of HB-PU are affected by some factors. Such as the molecular weight and content of soft segment, once the M-n of PEG soft segments is larger than the critical M-n (2000 g/mol), both the phase change enthalpy and temperature increase as M-n of PEG soft segment and soft segment content (SSC) increase. The influence of the microstructure of hard segment originates from diisocyanate and hyperbranched polyester polyalcohol, HB-PUs with regular microstructure and lower generation of hyperbranched polyester polyalcohol have high energy storage capability. Furthermore, the conditions of measurement affect the thermal characteristics of materials. (C) 2009 Wiley Periodicals, Inc. J Appl Polym Sci 115: 2228-2235, 2010