Abstract: Amphiphilic catalyst was synthesized and used in the aquathermolysis of extra-heavy oil to reduce its viscosity. The catalyst exhibits good performance in the aquathermolysis at 200℃ and the viscosity is reduced by 96.26% for the extra-heavy oil. The chemical and physical properties of heavy oil both before and after reaction were investigated by gas chromatography (GC), fourier transform infrared spectra (FT-IR), elemental analysis (EL), molecular weight analysis (VPO) and nuclear magnetic resonance (NMR). The results indicated that the content of resin and asphaltene is decreased and the average molecular weight of heavy oil and asphaltene is reduced after the catalytic aquathermolysis. The H/C ratio of heavy oil, resin and asphaltene is increased. The amount of sulfur in the heavy oil is also decreased after the treatment. A series of polymerization reactions take place in the course of aquathermolysis; the amphiphilic catalyst may depress the polymerization reactions while enhance the aquathermolysis. The pyrolysis of asphaltene plays a very important role in the viscosity reduction. During the aquathermolysis, many reactions such as pyrolysis, hydrogenation, ring opening, ring closing and desulfuration concerning C－S, C－N, C－O, C－C, C=S, C=O, C=N and C=S bonds are involved, which attributes to the reduce of viscosity and improvement of the heavy oil quality.