Two efficient viscosity reducers with the same ligand and different catalytic centers (Cu2+ and Fe3+) were prepared and characterized by Fourier transform infrared spectroscopy (FT-IR), and then used in catalytic aquathermolysis of six heavy oils. After that, Shengli extra-heavy oil (1.8 x 10(5) mPa s at 50 degrees C) was selected as the research object for an in-depth study of the same and different influences on the aquathermolysis of heavy oil catalyzed by the two catalytic ions. The compositions and structure of oil sample before and after reaction were analyzed by elemental analysis (EL), H-1 nuclear magnetic resonance (H-1 NMR), gel permeation chromatrography (GPC), and gas chromatography-mass spectrometry (GC-MS). The corresponding structural parameters were calculated on the basis of the improved Brown-Ladner methods. The compared results showed that the two catalytic ions mainly acted on the asphaltene of oil sample. In addition, the former mainly caused the depolymerization and cleavage of some bridge bonds of the macromolecular ring system, whereas the latter primarily led to the isomerization of side chains and ring-opening of heterocyclic rings. The former could be more suitable to catalyze the aquathermolysis of the heavy oil with high asphaltene than the latter for application.