The elemental analysis, molar conductance measurements, infrared and electronic spectra of certain novel chelates of Mn(II), Co(II), Cu(II), and Cr(III) ions with Schiff base generated from salicylaldehyde and thiourea have been examined. The elemental analysis results revealed that a 1:1 [M:L] ratio has formed. The molar conductance values obtained, demonstrated that all of the chelates are non-electrolytic. The chelation behavior, which occurs through the nitrogen and oxygen atoms of the ligand, was shown by the infrared spectrum data. The electronic absorption spectral data displayed the existence of π – π*, n- π* (HC≡N) transitions and the expected geometrical structures. By testing the effects of these Schiff base ligands on five species of bacteria in vitro, it has been found that Mn(II) chelate was very effective, Co(II) chelate had moderate effect and no effect of Cu(II) chelate was found on these bacteria. The effects of Mn (II) and Co(II) chelates increased with higher concentrations