Although light arenes such as benzene, toluene, and xylene in coal tar are widely used in industries, their amounts are relatively small. The catalytic cracking method for gaseous tar is one of the promising techniques for upgrading tar, and the amounts of light arenes are improved. Therefore, the catalytic upgrading of gaseous tar using two different catalysts is investigated in this study; the variations of light arenes before and after catalytic cracking are determined. More importantly, the variation of heavy compounds in gaseous tar is analyzed, and also the catalytic cracking mechanism is elucidated. The results show that the amount of benzene increases by 500% under the action of USY zeolite, and the amount of other compounds such as toluene, ethylbenzene, xylene, and naphthalene also increases by different degrees. However, Al/SBA-15 zeolite shows no obvious effect on gaseous tar upgrading. At the same time, the analysis results show that heavy compounds can be cracked over USY zeolite. Side chains are cleaved from aromatic rings, and aromatic rings are also cracked during the catalytic cracking reactions. Furthermore, light arenes are formed after the hydroxyl groups in phenols cleaved from the aromatic rings. (C) 2015 Elsevier B.V. All rights reserved.