The effect of sulfidation atmosphere (H2S/H-2 and H2S/N-2) on the morphology of (Co)MoS2 particles supported on gamma-Al2O3 was studied and the prepared catalysts were evaluated in selective hydrodesulfurization (HDS) of FCC gasoline. It was found that the selectivity of the CoMo/gamma-Al2O3 catalysts sulfided in H2S/N-2 was 1.8 times as high as that sulfided in H2S/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 H2S/N-2 could effectively weaken the strong interaction between the gamma-Al2O3 support and active components, thus inducing the decisive influence on the morphology of MoS2 particles. The MoS2 morphology differences could better explain the HDS selectivity. The CoMo/gamma-Al2O3 catalyst sulfided in H2S/N-2 showed significantly longer slab lengths of supported MoS2 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 MoS2 slabs. Crown Copyright (C) 2013 Published by Elsevier B.V. All rights reserved.