This study investigated the degradation of three nonsteroidal anti-inflammatory drugs (NSAIDs) (diclofenac (DCF), ibuprofen (IBP) and naproxen (NPX)) by UV/persulfate (UV/PS) in pure water and the influence of wastewater on UV/PS performance. Three NSAIDs have no obvious removal in the PS system, while they all showed a decrease in the UV system, and DCF showed the most significant decrease among the three NSAIDs in the UV system. The degradation of NSAIDs in UV/PS system followed the pseudo first-order degradation kinetics, and the kinetic constants orders are: k(DCF) > k(NPX) > k(IBP). SO4-center dot contributes more than center dot OH in NSAIDs degradation according to tertiary butanol and methanol inhibition tests. According to the degradation products detected by LC-MS, hydroxylation and decarboxylation are main pathways in NSAIDs degradation, and dechlorination is also a main path in DCF degradation. When UV/PS was used to dispose effluents spiked with NSAIDs solution (DCF, NPX, IBP, 0.1 mu M each), 10 times of PS dosage and 6 times treatment time were needed to get the same removal in pure water. The water quality parameters (i.e., natural organic matter (NOM), HCO3-, Cl- and NO3-) affects the degradation of NSAIDs by UV/PS. The degradation efficiency of NSAIDs was inhibited in the presence of humic acid and HCO3-. Meanwhile, Cl- and NO3- barely influenced the degradation efficiency.