Hydrotreating catalyst NiMo/Al2O3 was modified by adding nano-sized zeolite beta and by hydrothermal treatments. The catalysts were characterized by BET, XRD, Pyridine-IR, Si-29 NMR, Al-29 NMR and TEM. The results showed that the addition of nanobeta could significantly enhance the hydrodesulfurization (HDS), hydrogenation, and hydrocracking abilities of the NiMo catalysts. The catalytic performance decreased in the order NiMo(C) > NiMo(15)> NiMo(D) > NiMo(7.5)>> NiMo/Al2O3. The presence of nanobeta could strengthen acid sites which facilitated the abilities of hydrocracking and removal of sulfur-containing compounds, especially those of refractory nature. Introduction of nanobeta could also induce the synergetic effect between NiMoS and the support material with thicker NiMoS slabs. This morphology change might be responsible for the improvement in hydrogenation. It was observed that hydrothermal treatment conditions could affect the acidity and the NiMoS morphology of the catalysts, which in turn alter the catalyst hydrogenation ability. (c) 2012 Elsevier B.V. All rights reserved.