The morphology-performance relation is of great importance for designing a catalyst with high performance in the selective hydrodesulfurization (HDS) of fluid catalytic cracking (FCC) gasoline. Herein, we report a simple one-pot hydrothermal method to prepare the unsupported MoS2 catalysts with controlled morphology by adjusting the pH values and using different precursors. It is found that smaller MoS2 crystallites are produced when the pH value decreases in the synthetic process. With the increased MoS2 crystallite size, the HDS selectivity factor (SF) increases from 1.46 to 1.52 for non-promoted MoS2 catalysts, and from 13.96 to 19.69 for Co-promoted MoS2 catalysts. On the other hand, for MoS2 catalysts with similar stacking, the MoS2 with longer slab length exhibits improved HDS selectivity (SF from 2.90 to 2.99). These results confirm that the slab length instead of the stacking for MoS2 particles is more important to influence the HDS selectivity. Due to the fact that the corner sites could catalyze both HDS and HYD reactions while edge sites only catalyze the HDS reaction, thus increasing the edge/corner ratio by preparing (Co)MoS2 catalysts with longer MoS2 slab length is an efficient way to improve the selectivity in the selective HDS of FCC gasoline.