A new tetra dentate Schiff base ligand has been synthesized from condensation of compound (1): [( 4 -((1-H-imidazol-2-yldiazenyl)-1,5-dimethyl-2-phenyl-1Hpyrazol-3(2H)-one)]with compound (2) thio semicarbazaide. The general formula of complexes are [M(L)]Cl2 Where. M= Co(II) ,Ni (II)and Cu(II)Zn(II) are reported. The geometry structures of ligand and the complexes were determined through Fourier-transform infrared spectroscopy (FT-IR), Mass spectra, X-ray diffraction analysis, Ultra violet-Visible(UV-Vis), Proton nuclear magnetic resonance(1H NMR) spectral studies, magnetic moment measurement, elemental analysis, and molar conductance. These studies revealed square planar geometries for Ni(II)and Co(II) and Cu(II)complexes, except the Zn(II) complex was a tetrahedral geometry around the central metal ion. Complex formation studies via molar ratio and continuous variation methods were consisted to those found in the solid complexes with a ratio of (M:L) as (1:1) . Stability constant of complexes were calculated by spectrophotometric methods. Hyper Chem-8 program has been used to predict geometries structures of compounds in gas phase. The heat of formation (∆Hf) and binding energy (∆E b) at 298 K for the metal complexes were calculated by PM3 method. Biological activity studies of the ligand and their metal complexes against several organisms, bacteria Gram positive G(+ve)staphylococcus aureus and bacteria Gram negative G(- ve)Escherichia coli, klebsiella pneumonic, In addition to fungi like Aspergillus Niger, Rhizoclonia bataicola and Aspergillus flavus , are reported. Compounds exhibited the high activity on the growth of all types microorganisms in this study. This may be attributed to the impact of both the chelate effect of Schiff bases ligand and the role of the metal in these complexes.