Abstract: The influence of o-cresol on HDN of quinoline, HDS of DBT and HDA of 1-methylnaphthalene were investigated over a commercial catalyst in a fixed bed micro-reactor. The results suggest that o-cresol could strongly inhibit the HDN reaction of quinoline, HDS of DBT and HDA of 1-methylnaphthalene. The inhibition effect increases with the increasing content of o-cresol, which is resulted from the competitive adsorption between o-cresol and quinoline, DBT, and 1-methylnaphthalene. The presence of o-cresol has little effect on product selectivity. The hydrogenation is favored for aromatic ring without side chain, which is accounted for the steric effect.