The catalytic activities of CoMo and NiMo sulfides supported on Al2O3, and their modifications with P2O5 (3 wt%), ZrO2 (20 wt%), and B2O3 (15 wt%) were observed in the hydrodesulfurizations of 4,6-dimethyldibenzothiophene (4,6-DMDBT) and real feedstocks of gas oil (GO) and light cycle oil (LCO). Several catalysts of the higher transalkylation and hydrogenation activities exhibited the higher activity for HDS of GO and LCO as well as 4,6-DMDBT in the model solvent than in conventional commercial alumina-supported NiMo and CoMo catalysts, although the improvement was somewhat limited with the real. feedstocks. The transalkylation activity enhanced by the addition of the second oxide appears to correlate with the enhanced activities of HDS of 4,6-DMDBT and hydrogenation of naphthalene. Roles of the second oxide and inhibition behavior of aromatics and H2S are discussed on the basis of the foregoing results.