Eleven new Cu(II), Ni(II), and Co(II) complexes (1–11) with thiosemicarbazones 1-phenyl-3-methyl-4-benzoyl-5-pyrazolone-4-R thiosemicarbazone (where R = CH₃,C₆H₅, C₅H₅N) (HL¹⁻³) were synthesized. The ligands was characterized by FT- IR, ¹H NMR, ¹³C NMR spectroscopy and X-ray diffraction. All the complexes were characterized by UV–Vis and FT-IR spectroscopy, molar conductivity, magnetic susceptibility measurements and elemental analysis. In addition, the copper (II) complexes were studied by EPR spectroscopy. Also, the crystal structures of complexes 1, 3, 6 and 7 were determined by single-crystal X-ray diffraction analysis. The copper atom exhibits a distorted square-planar coordination environment in the complex 1 provided by one molecule of deprotonated ligand and one chloride anion, while in the complex 6 show a distorted square-pyramidal coordination geometry. In the complexes 3 and 7, the nickel atom exhibits a slightly distorted octahedral O₂N₂S₂ coordination provided by two molecules of tridentate deprotonated ligand. The in vitro antiproliferative activity of the ligands and metal complexes was screened on human leukaemia HL-60 cells. It was noticed a significant inhibition of growth of malignant cells HL-60 in the case copper complexes 2 and 5 with IC₅₀ values of 0.24 μM and 0.36 μM, respectively.