PURPOSE: To obtain with good efficiency a pitch-containing composition of high uniformity in physical properties by heat-treating a pitch precursor composition or a mixture of this composition, an aggregate and a dispersant by means of a static thermal reactor combined with a radiational heating means.

CONSTITUTION: A process for subjecting a heat-treated pitch or mesophase- containing pitch precursor composition and/or a mixture of this composition and an aggregate to a heat reaction of heating the composition to 300-5000°C in a high-temperature inert gas atmosphere, which comprises supplying thermal energy by radiational heat transfer from a thermal energy generator containing a heat reaction vessel with an open top and without mechanical agitator to the pitch-precursor-containing composition or the mixture of this composition, the aggregate and optionally a dispersant for this aggregage and contained in the abovementioned heat reaction vessel.