Reactions of ammonium thiomolybdate under mild hydrothermal conditions were studied, and the range of conditions leading to the dispersed MoS2 product has been determined. The morphology and the catalytic properties of the hydrothermal MoS2 preparations have been compared with thos of reference MoS2 proposed from the thermal decompostion of thiosalts. It has been shown that the length of the slabs and their stacking number of the crystallites of hydrothermal MoS2 preparations differ considerably from those in the reference sulfides. The morphological differences strongly influence the hydrogenation to hydrodesulfurization activity ratio in these systems.