Four molybdenum(VI) thiosemicarbazonato complexes have been synthesized and characterized. The dinuclear complexes [(MoO 2 L 1 ) 2 ] (1) and [(MoO 2 L 2 ) 2 ] (3) have been prepared by the reaction of [MoO 2 (acac) 2 ] with 2-hydroxyacetophenone N(4)-cyclohexyl (H 2 L 1 ) and N(4)-phenyl (H 2 L 2 ) thiosemicarbazones in alcoholic medium. Mononuclear dioxomolybdenum(VI) complexes of the type [MoO 2 L 1 py] (2) and [MoO 2 L 2 py] (4) have been prepared by the reaction of 1 or 3 with pyridine (py) in alcoholic medium. In all the complexes, molybdenum is coordinated by two terminal oxo-oxygen atoms, (O t ), oxygen, nitrogen and sulfur atoms from the principal ligand and by an oxygen atom from the second unit in 1, and by a nitrogen atom from pyridine in complexes 2 and 4. All complexes have been spectroscopically characterized. The molecular structures of complexes 1, 2 and 4 have been determined by the single crystal X-ray diffraction method.