A series of CoMo/graphene selective hydrodesulfurization (HDS) catalysts were prepared using the hexamethonium bromide-assisted hydrothermal method, and the influences of the hexamethonium bromide/Mo molar ratio and the CoMoS/MoS2 ratio on the HDS activity and selectivity were investigated. The results show that the k(HDS) value (2.76 x 10(-7) mol g(-1) s(-1)) of thiophene and the HDS selectivity factor (13.6) over the as-prepared catalysts were 1.3 times and 1.6 times greater than those over the CoMo/graphene prepared using the conventional impregnation method. The higher HDS activity and selectivity of the as-prepared catalysts result from the higher dispersion of Mo species and the higher CoMoS/MoS2 ratio compared to the CoMo/graphene prepared by impregnation. Among all the catalysts, the catalyst with a hexamethonium bromide/Mo molar ratio of 6.0 presents the highest HDS selectivity due to its highest ratio of edge to corner Co atoms in CoMoS with a superior CoMoS/MoS2 ratio. The present investigation provides a route for developing highly selective HDS catalysts using graphene as support by adjusting the hexamethonium bromide/Mo ratio to finely tune the morphology of the active phases.