Abstract: The effect of ultrasonic pre-treatment, followed by hydrotreating, on the status of association and structure of asphaltene was examined. The results indicate that ultrasonic treatment can change the asphaltene structure, but not the content of chemical elements. The structure changes caused by ultrasonic pre-treatment include the reduction of association number and increase of the branching degree through opening the naphthenic ring of asphaltene. Ultrasonic treatment reduces the molecular weight and the structure parameters of asphaltene, such as RT, RA, RN, CA and Dy. The distribution and types of hydrogen atoms are also changed. The molecular weight and parameters of fA, CAP, n, RT, RA, CA, Dy, BI of hydrotreated asphaltene increases because the occurrence of bridge bond rupture, dealkylation and condensation during the residue hydrotreating, while σ, H/C, nsw and X/n are decreased. These changes in structure and reactivity of asphaltene are helpful to residue hydrotreament. The functions of ultrasonic pretreatment are reinforced by hydrotreating. The structure of hydrotreated asphaltene was more complicated and the associating number of molecule even reaches 7 to 11.