In this study, Schiff base is synthesized through the reactance of di-o-bromobenzylacetone with thiosemicarbazide by acid-catalyzed condensation reaction (Aldol condensation). And using the novel Schiff base to prepare three metal complexes by reacting divalent transition metals (nickel, copper, iron) with the synthesized Schiff base. The prepared compounds were characterized by mass spectrometer, infrared spectrophotometer (FTIR), visible-ultraviolet rays (UV-Vis) and both 1H and 13C nuclear magnetic resonance spectrometer (NMR). The molar conductivity and magnetic susceptibility of the synthesized metal complexes were also measured. The cytotoxicity of the synthesized metal complexes against human breast cancer cell line MDA-MB231 was also measured in-vetro. All of the metal complexes were non-electrolyte and the predicted shape of these metal complexes is tetrahedral geometry. Results obtained from in-vetro cytotoxicity against breast cancer cell line type MDA-MB231 type showed that copper complex had best cytotoxicity with IC50 equal to 18.5µM .