Reactive oxygen species (ROS) are increased in inflammatory bowel disease (IBD) and have been implicated as mediators of intestinal inflammation. We investigated the hypothesis that N-acetylcysteine (NAC) as a glutathione (GSH) precursor attenuates disease progression in a murine dextran sodium sulfate (DSS)-induced colitis model. A colitis model was induced by adding 5% DSS into the drinking water for 7 days. BALB/c mice were injiciatur enema with saline, 5-ASA, N-acetylcysteine, respectively, and free drinking water as control group. DSS-treated mice developed severe colitis as shown by bloody diarrhea, weight loss, and pathologic involvement. Colon lengths were significantly decreased in DSS-treated mice with decreased GSH activity too (P < 0.01). ROS in the colon, the level of interleukin 1 beta (IL-1 beta) in colonic mucosa, serum tumor necrosis factor a (TNF-alpha), MPO, and MDA were significantly increased in DSS-treated animals (P < 0.01), with decreased PON1 activity (P < 0.01). However, NAC significantly decreased colonic MPO activity, ROS, TNF-alpha and IL-1 beta levels and increased PON1 activity and GSH concentration. Moreover, NAC attenuated the macroscopic colonic damage and the histopathologic changes-induced by DSS while similar to 5-ASA group. These results suggest that NAC may be effective in the treatment of colitis through its up-regulating PON1 and scavenging oxygen-derived free radicals.