New Schiff base ligand (E)-6-(2-(4-(dimethylamino)benzylideneamino)-2-phenylacetamido)-3,3-dimethyl-7-oxo-4-thia-1-azabicyclo[3.2.0]heptane-2-carboxylic acid = (HL) Figure(1) was prepared via condensation of Ampicillin and 4(dimethylamino)benzaldehyde in methanol .Polydentate mixed ligand complexes were obtained from 1:1:2 molar ratio reactions with metal ions and HL, 2NA on reaction with MCl2 .nH2O salt yields complexes corresponding to the formulas [M(L)(NA)2Cl] ,where M = Fe(II),Co(II),Ni(II),Cu(II),and Zn(II) and NA=nicotinamide. The 1H-NMR, FT-IR, UV-Vis and elemental analysis were used for the characterization of the ligand. The complexes were structurally studied through AAS, FT-IR, UV-Vis, chloride contents, conductance, and magnetic susceptibility measurements. All complexes are non-electrolytes in DMSO solution. Octahedral geometries have been suggested for each of the complexes. The Schiff base ligands function as tridentates and the deprotonated enolic form is preferred for coordination. In order to evaluate the effect of the bactericidal activity, these synthesized complexes, in comparison to the un complexed Schiff base has been screened against bacterial species, Staphylococcus aureus,Escherichia coli and the results are reported.