A series of NiMoS catalysts supported on USY-zeolite coated with different amounts of alumina were prepared and evaluated for deep hydrodesulfurization (HDS) of gas oil using a flow reactor system in single- and dual-bed configurations. The performance of these catalysts was compared to the conventional HDS catalyst as well as to NiMoS catalyst supported on physical mixture of alumina and USY-zeolite. Physically mixed alumina and USY zeolite showed high HDS activity, but it was accompanied with significant cracking of hydrocarbons. Activity and kinetic analysis showed that heavy coating of alumina on the zeolite resulted in much lower HDS and cracking activity. On the other hand, very light coating of alumina on the zeolite resulted in catalytic behavior similar to that of physical mixture of USY-zeolite and alumina. The general trend was an increase in HDS as well as hydrocracking activity with the decrease in amount of alumina coating over zeolite. Changes in product density, aromatic content, mid-boiling point, cetane index, and molecular weight also reflected this trend. The results of this study indicate that catalysts with neither too low nor too high amount of alumina coating on the USY zeolite are suitable to achieve the balance between high HDS and low cracking activities. The highlight of the present study is that it confirmed the deep HDS activity of USY containing alumina supports in the flow reactor system which is industrially applied. In addition, the stability test confirmed the long-term performance of alumina-coated zeolite catalyst. (C) 2013 Elsevier B.V. All rights reserved.