Abstract: Dagang vacuum residue was separated into four fractions (saturates, aromatics, resins, and asphaltenes, known as SARA) by chromatography. The features of molecular structure of aromatics, resins and asphaltenes were investigated by ruthenium-ion-catalyzed oxidation (RICO), where involatile acid products were methylated with excess diazomethaneether and volatile acids were esterified with phenacyl bromide. Based on GC-MS and GC analysis of these esters, homologous series of n-alkanoic acids (C4~33), α,ω-di-n-alkanoic acids (C3~24) and benzenepolycarboxylic acids were determined. The results indicate that the number of n-alkyl groups and polymethylenes connected to aromatic carbons decreases with an increase of the substituent chain length; it is characterized by an even-to-odd carbon number preference. Asphaltenes have relatively more short (C16) alkyl chains attached to aromatic carbons than resins and aromatics. Benzenedi through hexacarboxylic acids occurred in the RICO products prove the presence of polycyclic aromatic structure and can give a sight on the major mode of aromatic condensations in the fraction sample. The aromatic nuclear in asphaltenes have more peri-condensation structure units than that in aromatics. Cata-condensation modes are more abundant in aromatics.