Abstract: The molecular weights of asphaltene, resins and aromatics in Daqing, Shengli, Gudao and Liaohe vacuum residua were determined using benzene, chlorobenzene and nitrobenze as solvents, respectively. The molecular sizes of these sub-fractions were calculated according to a spherical molecular model, and the micellar particle model for asphaltene in vacuum residua was built. It is shown that primary asphaltene molecule size is about 3.8 nm～5.0 nm, 3.2 nm～3.7 nm and 2.8 nm～3.2 nm respectively in benzene, chlorobenzene and nitrobenzene solvents. The micellar sizes of asphaltene are about 10.0 nm～11.0 nm in Daqing, Shengli and Liaohe vacuum residua, and about 9.0 nm～10.0 nm in Gudao vacuum residuum.