Eight new mixed ligand complexes of dioxomolybdenum(VI) with 2-hydroxy-3-methoxy/3,5-dibromo benzaldehyde 4-phenyl/ethyl-S-methyl/butyl thiosemicarbazones (L) were synthesized. The complexes of general formula [MoO2LD] (D: methanol, pyridine) were characterized by elemental analysis, IR, UV, and H-1-NMR spectroscopy. The structure of 3a was also determined by X-ray single-crystal diffraction. The thiosemicarbazone ligands are coordinated to dioxomolybdenum(VI) center through ONN set and the sixth coordinated site of the molybdenum is occupied by the second ligand (D). The in vitro antimicrobial activities of all thiosemicarbazones and their dioxomolybdenum(VI) complexes were tested against Candida albicans, Escherichia coli, Pseudomonas aeruginosa, and Staphylococcus aureus.