Gamma-irradiation induced degradation of dexamethasone (DEX) in aqueous solution was investigated under different conditions. The results indicate that low-concentration DEX could be effectively decomposed during gamma irradiation. H2O2 and Fenton reagent were favorable for DEX radiolytic removal. However, DEX radiolysis was restrained in the presence of NO3-, CO32-, 2-propanol and tert-butanol. DEX radiolytic degradation was in accordance with the pseudo first-order reaction kinetics. The rate constant ratios of OH, e(aq)(-) and H-center dot towards DEX degradation could be calculated as k(OH): k(eaq-): k(H) = 10:1.5:1. Besides, it is observed that radiolytic degradation of DEX restrained algae growth. Finally, LC-MS analysis was employed to identify the intermediates and Gaussian 03 software was used to optimize DEX geometry structure. On the basis of LC-MS analysis and Gaussian calculations, we attributed DEX radiolytic removal to (OH)-O-center dot oxidation, (OH)-O-center dot radical substitution and direct cleavage of DEX molecules. (C) 2016 Elsevier B.V. All rights reserved.