Cancer is a worldwide public health problem, and it is the second leading cause of death in the world. Current drugs on the market have a number of insufficiency, with side effects being the most striking1,2. Therefore, the search for new drugs that are more effective and that reduce problems related to side effects has been widely explored. In the present work, new ruthenium (II)/phosphine complexes containing mercapto ligands were synthesized and characterized. The compounds, with general formula, [Ru(N-S)(cdppen)(bipy)], were synthesized from the precursor cis- [RuCl2(cdppen)(bipy)] (cdppen = 1,2-bis(diphenylphosphino)ethylene; 2,2'-bipyridine (bipy); N-S = 2-mercapto pyrimidine, 2-mercaptopyridine or 2-mercaptothyazoline ligands), Scheme1. The complexes were characterized by several techniques: molar conductivity, FTIR spectroscopy, cyclic voltammetry, 1H, 13C and 31P{1H} NMR, and monocrystal X-ray diffraction. Conductance measurements in dichloromethane indicated that the complexes are 1: 1 electrolytes (complex 1 = 43.0 ohm-1 cm2 mol-1 and complex 2 = 36.7 ohm-1 cm2 mol-1 at 25 °C), confirming the presence of PF6 - counter ion in the compounds. Based on the 31P{1H} NMR spectra, it is possible to observe the expected doublets, confirming presence of complexes of AX systems. The voltammograms of the complexes, obtained in dichloromethane (1 mmol of PTBA), showed the oxidation potentials of RuII/RuIII, presenting quasi-reversible processes. The complex with the 2-mercaptopyrimidine ligands, is cytotoxic (IC50 = 1.21 ± 0.69 µM) against tumor line MDA-MB-231.The cytotoxicity of the complexes, in cancer and non cancer cells are in progress, and will be showed.