Synthesis of new oxomolybdenum (V) and dioxomolybdenum (VI) complexes with 2-imidazolyl mercapto aceto hydrazone (LH2; structure I) derived from 2-imidazolyl mercaptoaceto hydrazide and o-hydroxy aromatic aldehyde are reported. The complexes have been characterised by elemental analysis, molar conductance, magnetic susceptibility, IR, UV-vis, EPR and 1H NMR spectral studies. The physicochemical studies and spectral data indicate that LH2 acts as monovalent ONO donor containing chelating agent, thus exists in keto form. From analytical data the stoichiometry of the oxomolybdenum (V) and dioxomolybdenum (VI) complexes have been found to be 1:1 (metal: ligand) ratio with the general formula [MoO(LH)Cl2] and [MoO2(LH)Cl] respectively. Dioxomolybdenum (VI) complexes are diamagnetic, contain MoO2 2+ species, where as oxomolybdenum (V) complexes are paramagnetic and all the complexes are non-electrolytic nature. ESR spectral data suggest that monomeric nature of oxomolybdenum (V) complexes with distorted octahedral geometry. The thermal stabilities of the complexes have been studied by thermogravimetric techniques. The hydrazones and oxomolybdenum (V) and dioxomolybdenum (VI) complexes were screened for their in vitro antibacterial activities against Salmonella paratyphi and Bacillus cirroflagellosus. Antibacterial studies of the present complexes show that the oxomolybdenum (V) complexes were more potent bactericides than the ligand and the dioxomolybdenum (VI) complexes.