A polyacene-based oligomer was synthesized by reaction of diphenyldiacetylene under high pressure (pressure : 0.1 GPa; temperature : 250 degrees C; time : 5 h). Annealing of the polyacene-based oligomer was carried out (temperature : 300-800 degrees C; time : 5 h). Gas analysis, BET surface area measurement, Raman scattering, X-ray diffraction, elemental analysis, C-13-NMR, and conductivity measurements were performed to characterize the structure of the product. The oligomer was annealed with the appearance of mainly hydrogen. The WC of the product decreased with increasing annealing temperature. The Raman band is observed at 1610 cm(-1) assigned to a doubly degenerate deformation vibration of the carbon hexagonal ring. The additional band observed at 1340 cm(-1) is attributed to the size effect. X-ray diffraction indicated that the product had no sharp peak because of the disordered carbon structure.