New organometallic compounds of Mn(II), Fe(III), Ni(II), Cu(II), and Zn(II) (1Z,2Z)-N1,N'1,N2,N'2-tetrakis(2-hydroxyphenyl) oxalimidamide ligand have been prepared and characterised using elemental and spectral analyses, magnetic moments, conductance, and thermal analysis (DTA and TGA). The complexes were non-electrolytes based on molar conductance in DMF solutions (11.2 - 14.5 ohm-1 cm2 mol-1). The ESR spectra of solid Cu(II) complexes (2), (3), and (4) revealed an axial type symmetry, indicating a b&a d(x2-y2) ground state with a substantial covalent bond character, whereas Mn(II) complex(5) revealed an isotropic type.Furthermore, the spectra corroborated the octahedral structure of the metal ions. The complexes were tested for cytotoxicity as antitumor agents against breast cancer using the MCF-7 cell line. Cu(II) complex (2) outperformed Cu(II) complex (1) in terms of cytotoxicity against breast malignant cells. Cu(II) complex (2) had a stronger cytotoxic effect on breast malignant cells, with an IC50 of 7.5 ug.IC50 for a reference medicine (cisplatin) was 5.71 ug, Cu(II) complex (2)>Pb(II) complex (10)>Zn(II) complex (9), Cu(II) complex (4)>Cu(II) complex (3), Zn(II) complex (8)>Fe(III) complex (6)>Ni(II) complex (7) with IC50 within range (21-7.5 ug). Complexes outperformed the parent ligand and the standard medication (cisplatin) in terms of activity. These investigated complexes are potential anticancer drugs for the MCF-7 breast cancer cell line.