Abstract: A series visbreaking experiments were carried out with four types of vacuum residues on LPEC static tester to investigate the effect of reaction temperature and time on the visbreaking ratio and the contents of C7 insolubles in visbroken residue oils. The results indicate that the visbreaking ratio varies with different residue oils under the same operating conditions and that there is a maximum visbreaking ratio as the reaction time increases under the same reaction temperature for the same oil. Under mild reaction conditions, little difference of visbreaking results for different heavy oils is found. However, great changes are observed under severe operating conditions and the visbreaking ratio decreases sharply, showing the stable structures of resins in residue oils are destroyed. The contents of C7 insolubles in visbroken residue oils also vary significantly with reaction temperature and time.