PURPOSE: To obtain an amorphous carbon material having improved gaseously transmissible property by subjecting a carbonaceous material to a specific treatment, heating and baking the produced aqua-mesophase or amphiphilic carbonaceous mesophase in an inert atmosphere and, as necessary, heat-treating the product at a high temperature.

CONSTITUTION: A carbonaceous material having an H2 content of ≥2wt.% and produced by the heat-treatment of a raw material such as coal tar pitch is treated with an acid or oxidizing agent such as HNO3, H2SO4, mixture of HNO3 and H2SO4, H2O2 or KMnO4 and the oxidation product is filtered, washed with water and dried. The dried material is dissolved in water, a basic aqueous solution or an organic solvent, the solution is filtered to remove insoluble components and the dissolved components are precipitated again and filtered to obtain an aqua-mesophase or amphiphilic carbonaceous mesophase. The mesophase is heated in a non-oxidizing atmosphere to ≥600°C at a heating rate of ≤30°C/h in the case of the treatment with an acid or an oxidizing agent containing HNO3 or at an arbitrary heating rate otherwise to effect the carbonization and baking of the mesophase. As necessary, the carbonized product is heated at a high temperature (≥2000°C) to obtain the objective amorphous carbon material having isotropic fine structure.