Degradation of imidacloprid in dilute aqueous solution irradiated by 60Co γ-rays was studied. The samples before and after irradiation were detected by high performance liquid chromatography (HPLC), ion chromatography (IC) and high performance liquid chromatography-mass spectrometry (HPLC-MS). The experimental results show that the degradation rate increases gradually with the absorbed dose and reach 100% at the absorbed dose of 1.56 kGy. Imidacloprid irradiation degradation products include four kinds of inorganic ions of Cl-, NO2-, NO3-, and NH4+ and four kinds of organic products of 2-chloro-5-imidazol-1-ylmethyl-pyridine, 1-(6-chloro-pyridin-3-ylmethyl)-1,3-dihydro-imidazol-2-ylideneamine, mono-hydroxylated imidacloprid and double-hydroxylated imidacloprid. Oxidative free radicals ?OH couldattack C−Cl bond, N−N bond, C=N bond and C−H bond of imidacloprid molecule easily.Cited