The reaction of the hydroxy radical with thymidine and poly-hydroxy benzenes; i.e., catechol, resorcinol, hydroquinone, and pyrogallol, was studied by ESR spin trapping combined with the UV-A photolysis of hydrogen peroxide. The obtained relative reaction rates reasonably agreed with those previously obtained by pulse radiolysis. Electron distribution in the HOMO obtained by DFT calculations also supports the resulting order of reactivity of the polyphenols.