A Synthesized from a new neutral tridentate N2O Schiff base 4-(4-hydroxy-2-methoxybenzylidene)amino)-1,5-dimethyl-2-phenyl-1,2-dihydro-3H-pyrazol-3-one with serine amino acid ligand forms stable complexes with many ions such as Co (II), Ni (II), Cu (II),Zn(II), and Cd (II). The complexes were recognized in term of their elemental analysis, 1H-NMR, UV-Vis, XRD, thermal analysis (T.G,DTA,DSC), and calculation theoretical studies (DFT) were used to characterize the complexes. The ligand acts like a tridentate chelating agent according to physicochemical and spectral results, the ligand acts like a tridentate chelating agent IR, UV-Vis, molar conductivity, and magnetic susceptibility measurements, all refer to an octahedral geometry the general composition of all complexes [M(L)2] is (M=Co(II), Ni(II). Cu(II),Zn(II), and Cd(II) L= (K4-AMetB-Ser). Concluded through studies that,the coordination sites were established to be oxygen of the carboxyl COO- and two atoms nitrogen of the azomethine (CH=N) group based on the studies. The complexes non-electrolytic nature is verified by the lower conductivity data. Finally the antibacterial activity of the ligand and its complexes was tested against Staphylococcus aureus, Escherichia coli, and Pseudomonas aereuguinosa it was found that these compounds show different activity of inhibition bacteria growth.