Ciprofloxacin (CPFX) and enrofloxacin (ENFX), two representatives of fluoroquinolones (FQs), pose potential threats to health for their wide exposures in environment. The aim of the study is to characterize the harmful effects of oxidative stress induced by CPFX and ENFX from the structure and function of catalase (CAT), a vital enzyme involved in protection against oxidative damage. The cellular tests firstly confirmed an enhanced oxidative stress in FQs treated erythrocytes from the depletion of GSH contents and decrease of CAT activity. Besides, CPFX posed more of an oxidative threat than ENFX. During the spectroscopic and computational investigations, both FQs could bind into its central cavity with only one binding site and interact with Arg 65, Arg 362 and His 363 mainly through electrostatic forces. Furthermore, the binding of two FQs not only caused the conformational and micro-environmental changes of CAT, but also inhibited its molecular activity, consistent with the cellular activity measurements. All these results suggested that the structural and functional changes of CAT were closely associated with increased risk of oxidative stress induced by both FQs. The established methods in this work can help to comprehensively understanding the oxidative stress-induced cellular damage of other pollutants via antioxidant effects. (c) 2013 Elsevier B.V. All rights reserved.