Results of quantitative studies of radiosensitivity and radiolytic mechanisms of methionine in aqueous solution exposed to gamma-irradiation are presented. The products of methionine, methionine sulfoxide, methionine sulfone, α-amino-n-butyric acid, homoserine, homocysteic acid and homocystine, which were irradiated separately under identical conditions were studied using an amino acid analyzer. The probable pathways on the radiation decomposition of methionine are discussed.