Abstract: The absorbance, fluorescence and cyclic voltammetric methods as well as agarose gel electrophoresis were used to study the interaction of the antitumor compound Et₂SnCl₂(phen) with DNA. The results indicate that Et₂SnCl₂(phen) mainly reacts electrostatically with the phosphate backbone of DNA. There also exists an intercalation into the doublehelix of DNA through the phenanthroline group of Et₂SnCl₂(phen). At high concentration Et₂SnCl₂(phen) can cause unwinding of DNA. The molecular action mechanism of Et₂SnCl₂(phen) with DNA was first proposed.