To improve the hydrodesulfurization activity while to minimize the hydrogen consumption from the hydrogenation of olefins is of importance for the deep desulfurization of gasoline. Herein, a series of Co/MoS2 +/- x catalysts were prepared by impregnating Co-promoter to MoS2 +/- x (x < 0.06) with controllably varied S/Mo atomic ratio. The S/Mo atomic ratio of MoS2 +/- x in Co/MoS2 +/- x catalysts influences the catalytic performance of Co/MoS2 +/- x in simultaneously thiophene hydrodesulfurization (HDS) and cyclohexene hydrogenation (HYD) reactions. With decreasing the S/Mo atomic ratio in Co/MoS2 +/- x, the HDS selectivity factor (k(HDS)/k(HYD)) increases to two times (from 37 to 89), although the catalytic activities of HDS and HYD decrease due to the low content of CoMoS phase. The higher selectivity of Co/MoS2 +/- x with lower S/Mo atomic ratio could be well explained by larger size of sulfide crystallites exposed lower corner sites. Therefore, a high HDS selectivity catalyst could be developed by properly controlling the crystal size of sulfide crystallites. (C) 2016 Elsevier B.V. All rights reserved.