Abstract: A method of manufacturing a heat-resistant expanded graphite sheet is characterized in that after an acid-treated graphite material obtained by treating a graphite material with a strong acid is compounded with a powder of an organic phosphorus compound and is agitated and mixed uniformly to obtain a mixture, this mixture is subjected to heating treatment for 1 to 10 seconds at temperatures of 950 to 1200° C. to produce cracked gas, that gaps between graphite layers are expanded by its gas pressure to obtain expanded graphite particles having an expansion rate of 200 to 300 times, and that these expanded graphite particles are subjected to pressure molding.