The effect of sulfidation atmosphere (H 2 S/H 2 and H 2 S/N 2 ) on the morphology of (Co)MoS 2 particles supported on γ-Al 2 O 3 was studied and the prepared catalysts were evaluated in selective hydrodesulfurization (HDS) of FCC gasoline. It was found that the selectivity of the CoMo/γ-Al 2 O 3 catalysts sulfided in H 2 S/N 2 was 1.8 times as high as that sulfided in H 2 S/H 2 , and the catalytic performance was mainly determined by the first sulfidation atmosphere after the impregnation of Mo. The characterization by XRD, HRTEM, XPS, TPR and FT-IR showed that the more completed sulfidation of Mo oxides in H 2 S/N 2 could effectively weaken the strong interaction between the γ-Al 2 O 3 support and active components, thus inducing the decisive influence on the morphology of MoS 2 particles. The MoS 2 morphology differences could better explain the HDS selectivity. The CoMo/γ-Al 2 O 3 catalyst sulfided in H 2 S/N 2 showed significantly longer slab lengths of supported MoS 2 slabs, which effectively decreased the number of active adsorption sites for olefins and thus suppressed the hydrogenation activity of olefins, leading to a desirable higher HDS selectivity. Therefore, a tailor-made catalyst with high HDS selectivity could be developed by optimally controlling the slab lengths of supported MoS 2 slabs.