The heat storage and phase transition behavior of a series of poly(vinyl alcohol)-g-octadecanol copolymers (PVA-g-C18OH) with apparent grafting ratios ranging from 283 to 503%, synthesized through "grafting to" method, has been investigated by Fourier transform infrared spectroscopy (FTIR), differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), wide-angle X-ray diffraction (WAXD) and polarized optical microscopy (POM). PVA-g-C18OH copolymers exhibit the better thermal stability against C18OH, and the thermal energy storage ability (Delta H(m)) is of dependence on the apparent grafting ratios. Compared with C18OH, the lower thermal storage efficiency possible is attributed to the less CH(2) groups entered into the crystalline domains and the frustrated mobility of the grafted C18 alkyl side chains between PVA backbones. The results show that PVA-g-C18OH copolymers have the better thermal stability and storage ability, which can be wildly applied in the aspect of thermal energy storage. (C) 2011 Elsevier B.V. All rights reserved.