Macrocyclic metal complexes viz., Co(II), Ni(II), Cu(II) and Zn(II) have been prepared using a macrocyclic Schiff base as ligand, which was derived from Isatin, 4-aminoantipyrine and o -phenylenediamine. Further, the complexes have been characterized by elemental analysis, magnetic susceptibility, molar conductance, mass spectrometry, FT-IR-, Far-IR-, UV-Vis-, EDX spectroscopy, 1 H NMR and 13 C NMR, ESR spectroscopy and SEM. The octahedral geometry of the complexes has been revealed by the spectral data of UV-Vis and ESR as well as by the results of the magnetic susceptibility measurements. Antimicrobial screening tests indicated that the Zn(II) metal complexes showed an excellent antimicrobial activity compared to the other studied metal complexes. The nuclease activity of the metal complexes showed that the Co(II) complex has effectively cleaved DNA. The optimized molecular structure, bond length, bond angle, dihedral angle, chemical reactivity and total energy have been evaluated using the density functional theory (DFT) with B3LYP functional level.