Bulk MoS2 catalysts were prepared starting from various Mo-precursors. The catalytic activity was investigated for hydrodesulfurization (HDS) of dibenzothiophene (DBT) with a batch sampler attached micro-autoclave reactor at 340 degreesC and 3 MPa H-2. In general, HDS activity was found to be inversely proportional to catalysts particle size. An interesting relationship was found between the average number of MoS2 stacked layer and the selectivity of HDS in which it passes through a minimum at small crystallite sizes of ca. 4 nm and then turned up with crystallite sizes larger than 5 nm irrespective of the starting catalyst precursors. Detailed kinetics is discussed. (C) 2003 Elsevier B.V. All rights reserved.