An ethylene bottom oil pi Inch from petroleum contains a high concentration of aromatic constituents and the formation rate of the quinoline increases with heat treatment time and temperature as a first order reaction when the pitch is treated above 400℃. The activation energy of the reaction, derived from the formation rate of the quinoline insolubles is 50.3 kcal/mol. The mesophase spheres formed by heat treatment at 410℃ coalesce hardly while the spheres growing at 430t show good coalesence to lead phase inversion between the mesophase structure and the isotropic pitch.