Abstract: HClO4-GICs were prepared by a chemical method using natural graphite flake, perchloric acid and concentrated nitric acid as host material, intercalating agent and catalyst, respectively. The GICs were exfoliated to make exfoliated graphite. Flexible graphite was made by compressive molding of the exfoliated graphite, and was characterized by mechanical and thermal/electrical testing. An orthogonal experimental design method was used to investigate the effects of reaction temperature and time, expansion temperature and the HClO4GIC volatiles on the exfoliation volume of the exfoliated graphite. It was found that HClO4GIC could be synthesized at temperatures from ambient to 100℃ by HClO4/HNO3 impregnation. The descending order of factors affecting exfoliation volume was reaction temperature, weight ratio of HClO4 to HNO3, reaction time and weight ratio of graphite flake to HClO4. Under the optimum conditions with the weight ratio of natural flake graphite∶perchloric acid∶nitric acid being 1∶4∶0.15, reaction time of 15min, and reaction temperature of 100℃, the exfoliated graphite obtained at 200℃ and 900℃ had exfoliation volumes of 360mL/g and 540mL/g respectively. With increasing density, the tensile strength of the flexible graphite increased, electrical resistivity decreased and the thermal conductivity increased. The thermal conductivity of flexible graphite is higher than a carbon/graphite composite with the same electrical resistivity.