The main purpose of this study is to elucidate the effect of catalyst on asphaltene molecular structure during hydrocracking of C-5-isolated asphaltene. Remained asphaltene and coke were obtained after hydrothermal and catalytic hydrothermal cracking of C-5-isolated asphaltene at 380-430 degrees C, using 1000 ppm Mo from Mo-octoate precursor. XRD and NMR analyses were used to investigate the change of molecular structure of asphaltene during the reaction. It was revealed that aggregation of asphaltene increased with increasing the reaction severity resulted in coke formation. The presence of catalyst reduced the aggregation of asphaltene molecules in comparison with the hydrothermal cracking. It was also observed that the average number of stacked poly-aromatic sheets in the remained asphaltene decreased with increasing the reaction temperature because of the transformation of high stacked asphaltene into coke during the reaction. Moreover, it was confirmed that the main reason for asphaltene aggregation was the reduction of steric hindrance of asphaltene molecules by the change in molecular structure of asphaltenes.