PURPOSE: The titled composition providing easily a non-fusible, insoluble, heat- resistant cured material by heat curing, obtained by blending a specific aromatic hydrocarbon compound with a thermally meltable formaldehyde polymer as a crosslinking agent in a specific ratio and reacting them in the presence of an acid catalyst.

CONSTITUTION: Firstly, (A) A raw material comprising an aromatic hydrocarbon compound (e.g., pyrene, etc.,) containing condensed polycyclic aromatic nuclei of ≥4 rings or a mixture comprising it as a main component is blended with (B) a thermally meltable formaldehyde polymer (e.g., trioxan, etc.,) as a crosslinking agent in such a way that a ratio of number of mols of the component B calculated as formaldehyde/average number of mols of the component A is 1.8W9. Then, the mixture is reacted in the presence of an acid catalyst (preferably protonic acid such as sulfuric acid, etc.,) under heating at ≥ the melting point of the component B, to give the aimed composition. The reaction under heating is usually stopped before the reaction product becomes a cured material.