gamma-Alumina-supported MoS3 nanoparticles (NPs) denoted as MoS3/Al2O3 were firstly synthesized by chemical deposition method, and then used as the "second support" for promoter Ni atoms to prepare a pre-sulfided bimetallic HDS catalyst denoted as CAT-MoS3 by the conventional impregnation method. Meanwhile, for comparison purpose, two bimetallic catalysts denoted as CAT-MoS2 and CAT-MoO3 with the same metal loadings were prepared using MoS2/Al2O3 and MoO3/Al2O3 as the starting material, respectively. Characterization and activity assessment show that, using MoS3 as the precursor not only promotes the resulting bimetallic catalyst with a much higher sulfidation degree of Mo species, but also realizes a better decoration of Ni atoms onto the edges of MoS2 nanoslabs. The dual effect guarantees the plentiful formation of Type II Ni-Mo-S active sites and thus remarkably enhances the hydrodesulfurization (HDS) activity. Compared with CAT-MoS2, CAT-MoS3 possesses very similar physical properties, microstructure and sulfidation degree of Mo species, however, due to its much higher decoration degree of Ni atoms, it holds a significantly enhanced HDS activity. Moreover, in comparison with CAT-MoS2, CAT-MoO3 exhibits a worse microstructure (more MoS2 nanoslabs with larger length and lower stacking) and a much lower sulfidation degree of Mo species, but it still holds much higher HDS activity, further implying that the decoration degree (i.e. promoting effect) imposes the most important impact on the HDS activity. It is rational and effective to modify the starting state of Mo species to enhance the promoting effect and thereof improve the catalytic performance.