This study focused on the degradation of the worldwide Non-steroidal Anti-Inflammatory Drug (NSAID) ibuprofen (IBP) by gamma irradiation. Factors affecting IBP degradation efficiency were examined. The results showed that IBP concentration decreased with an increasing absorbed dose. When IBP concentration of 28.3 mg/L and an absorbed dose of 1.1 kGy were chosen, IBP degradation value was 100%. The degradation process of IBP could be depicted by first order reaction kinetics when the absorbed dose was less than 0.9 kGy. 0.1% H2O2 and humic acid additives enhanced IBP degradation process, while 0.5% H2O2 additive restrained the degradation of IBP. The additions of CO32-, NO3-, CH3OH and thiourea restrained the degradation process. The pH value affected the IBP degradation. The degradation efficiency was more efficient under acidic condition than in neutral or alkaline media. The solution pH value became lower with increasing absorbed dose after gamma irradiation. High performance liquid chromatography (HPLC) and electrospray ionisation mass spectrometry (ESMS) techniques were employed to identify the IBP derivatives. The mono- and quadric-hydroxylated of IBP and the products due to the oxidation of propanoic acid, and isobutyl substituents of IBP were identified. (C) 2011 Elsevier B.V. All rights reserved.