The hydrodesulfurization (HDS) of thiophene and its derivatives by Mo-based catalysts shows significant economic benefits in crude oil processing and refining. Several Mo-based catalysts have been successfully used for HDS reaction despite of unclear catalytic mechanism. Thereby we use in situ FT-IR technique to investigate the adsorption of thiophene on the surface of supported and dispersed sulfided Mo catalysts. The results demonstrate that thiophene can be adsorbed on the catalyst surface through coordination of S atom, C=C and C-C with the unsaturated Mo(d+) sites located on the edge planes of MoS(2)-like structures, forming four different complexes. These adsorption manners were also proved by theoretical calculation with the density functional method (DFT). The calculated binding energy of eta(2)(S) complex is larger than other complexes, suggesting that thiophene preferred to being adsorbed on the catalyst surface through the coordination of C=C with unsaturated Mo(d+) sites. The formation of coordinated complexes can decrease the aromaticity of thiophene ring and weaken CAS bond, which could promote the HDS reaction. (C) 2011 Elsevier Ltd. All rights reserved.