Abstract: Based on experimental check of the theoretically deduced equations which are used to determine the composition of heavy oils without standards by HPLC, the ring distribution of aromatics and molecular weight distribution of the residue oil are studied. Two separate moving phases with different refractive indices but analogous eluting characteristics are used. According to two different chromatograms of the sample, the deduced equations are solved simultaneously for the individual concentration and refractive index of the components in the sample. It is shown that the relative error of the concentrations obtained is less than 4%. Benzene, naphthalene, anthracene, chrysene and benzopyrene are used as marking materials for different rings of aromatics in the determination of ring distribution, and the average eluting times of two adjacent peaks are taken as the beginning and end of limits of responses of aromatic fractions with different rings. Toluene and chloroform are used as eluents in gel permeation chromatography. The total linear correlation coefficient for molecular weights vs. eluting volumes using two different moving phases is 0.99. This method for differential characterization of the composition and distribution of molecular weights of heavy oils can be used as a new tool for the study of heavy oil chemistry and technology.