The structural characteristics of a pentane-insoluble asphaltene isolated from the vacuum residue of an Arabian crude mixture have been investigated by pyrolysis gas chromatography/ mass spectrometry (py/GC/MS), H-1/C-13 NMR, gel permeation chromatography (GPC), and matrix-assisted laser desorption/ionization time-of-flight (MALDI TOF) mass spectrometry. Assignments of NMR signals of the asphaltene have been discussed briefly on the basis of the information from the literature and compared with those of an aliphatic fraction isolated from the ruthenium ion catalyzed oxidation products of the asphaltene. The comparison data indicated that aliphatic substitution > C-1 on aromatics are little; however, most of the chain methylene groups are located within a polymeric-saturated fraction of the asphaltene. The average size of aromatic fused ring systems has been determined to be 4-5 for the sample. Pyrolysis tests implied that the asphaltene sample is constructed with relatively large polycyclic units connected by relatively strong bonds. Our results also support a view that asphaltene is the mixture of complex polydispersed molecules with large variation of molecular sizes.