In this paper, in order to enhance the thermal performance of paraffin in thermal energy storage, the graphene and exfoliated graphite sheet have been mixed with the paraffin to prepare composites. After the stability tests of dispersion, the scanning electron microscope (SEM), Fourier transform infrared spectroscope (FTIR), thermal conductivity analysis, differential scanning calorimeter (DSC) and thermogravimetric analyzer (TG) are applied to characterize the microstructure, chemical structure, thermal conductivity, enthalpy and stability of the materials, respectively. The results indicated that the thermal conductivity was able to be increased greatly with graphene or exfoliated graphite sheet. With the same mass fraction, the thermal conductivity of paraffin/graphene composite was greater than that of paraffin/exfoliated graphite sheet composite. Furthermore, when the mass fraction of graphene or exfoliated graphite sheet varied between 0-2.0 wt.%, the enthalpy of phase change material (PCM) composites rose firstly and then dropped down. (C) 2016 Elsevier B.V. All rights reserved.