The mononuclear complex, [Co(TAMEN)](ClO(4))(2) (DMSO), containing the Mannich base N,N'-tetra-(4-antipyrylmethyl)-1,2-diaminoethane (TAMEN) as ligand, was synthesized and characterised by conductometric, electronic and infrared spectroscopic properties. The single-crystal X-ray structure show the presence of two well defined units, [Co(TAMEN)](2+) and (ClO(4))(-). The complex cation contains cobalt(II) in the pseudo octahedral environment created by the N(2)O(4) donor set of TAMEN. The cobalt(II) complex have been screened for its cytotoxic activity against three cultured human cell lines established from hepatoma (Hep G2), breast (MCF-7) and lung (A549) cancers as well as on non-tumor bovine kidney (MDBK) cells. The cytotoxic activity of the ligand TAMEN was assessed on one tumor (Hep G2) and one non-tumor (MDBK) cell lines. The cobalt(II) compound was found to decrease in a time- and concentration- dependent manner the viability of tumor (A549, MCF-7, Hep G2) cell lines, while the ligand TAMEN expressed proliferative activity on hepatoma (HepG2) and bovine kidney (MDBK) cells, especially after prolonged incubation.