PURPOSE: To provide an electrically conductive organic high-molecular material having excellent resistance to thermal oxidation, by incorporating an electron- donating or accepting doping agent in a specified insoluble, influsible substrate contg. a polyacene skeleton structure.

CONSTITUTION: A powder such as sodium phosphate powder is mixed with an arom. condensation polymer composed of carbon, hydrogen and oxygen atoms obtd. by reacting an arom. hydrocarbon compd. contg. a phenolic hydroxyl group with an aldehyde. The mixture is molded and cured. The cured article is then heat-treated at 350W800°C in a non-oxidizing atmosphere and washed with water to remove the residual sodium phosphate, etc. and the thereby obtain an insoluble, infusible substrate having a ratio of H/C of 0.6W0.15 and a specific surface area of 600m2/g or above as measured by BET method. The substrate is doped with an electron-donating doping agent such as lithium or an electron- accepting doping agent such as fluorine to impart (semi-)electrical conductivity thereto.