This project is focused on study of a molecular mechanism of antitumor ruthenium complexes. Ruthenium complexes with dimethylsulfoxide ligands and complexes, their basic formula is HL[RuCl4L2], where L are nitrogen heterocycles. These chosen complexes sh ow inhibition effects against some metastases or colon tumors lines. The biological properties of the ruthenium complexes chosen for our studies are interesting in context of their using as cytostatics, which could be an alternative to clinically used p latinum drugs. The main target of antitumor action of the metal complexes of the platinum group including ruthenium complexes is DNA. The main topic of this project is therefore the study of a ruthenium complexes influence on DNA properties by using mod ern methods of molecular biophysics. On the basis of comparision our obtained results with data observed by other authors in recent works on DNA modified by cisplatin, the first cytostatic of this class used in clinic, we would like to suggest the struct