Solid fossil-fuel derived pitches serve as potential feedstocks for the preparation of high-performance carbons materials, which is, however, hampered by the lack of sound knowledge on the molecular composition and structure of pitches. Soxhlet extraction and ultrahigh-resolution Fourier transform ion cyclotron resonance (FT ICR) mass spectrometry were combined to characterize a petroleum pitch and a coal tar pitch, as well as their toluene-soluble and toluene-insoluble fractions. Important information can be gained on the chemical nature of polycyclic aromatic compounds such as pure hydrocarbons and various N-, O- or S-derivatives, as well as the relative abundance of each molecular structure in terms of carbon number vs. hydrogen number. This is the first time that the heteroatom-containing and pure hydrocarbon aromatics were clearly differentiated in such solid pitch samples. The differences among the toluene-soluble fraction, toluene-insoluble fraction, and unfractionated intact sample of both the petroleum pitch and coal tar pitch could be systematically compared at a molecular level. Insight into the molecular structures may provide a rational basis for the use of such carbon-rich materials for the fabrication of nanographenes, organic light-emitting diodes, and carbon fibers.