This study examined the effects on the radiolysis of magnesium-guanosine-5'-monophosphate complexes in deaerated aqueous solutions, investigated by Fourier transform infrared (FT-IR) spectroscopy. It was found that when the system was irradiated with a dose rate of 500 rad/min (low dose rate), the OH radicals, H atoms and hydrated electrons (eaq-) produced from radiolysis of water reacted mainly by addition to the double bonds C4 = C5 and N7 = C8 of guanine. When the dose rate was 23,800 rad/min (high dose rate) the electrons reacted further with the complex by addition to the carbonyl group, C6 = O, of guanine.