An animal study in rats and a cell culture study in normal human lung epithelial cells were conducted to evaluate the efficacy of N-acetyl-l-cysteine (NAC) in paraquat intoxication and associated inflammatory and oxidative stress. The effectiveness of post treatment was measured by the change of mortality rates and markers of oxidative stress, including glutathione, malondialdehyde and superoxide anion production. In addition, the levels of nitric oxide were also examined in both animal and cell culture system. NAC treatment does significantly increase the probability of survival in paraquat-intoxicated rats. It can suppress the serum malondialdehyde levels and production of superoxide anions, and conversely, augment total glutathione concentrations in all studying tissues significantly. Moreover, NAC treatment post in paraquat intoxication could reduce destruction of lung tissue, showing less inflammatory cell infiltration in interstitial stroma and mild vascular congestion. The levels of nitrite in serum and BALF were lower than those of the PQ-treated rats. Similarly, levels of iNOS expression and nitrite formation were significantly lower in normal human lung epithelial cells treated with PQ and NAC than PQ-treated alone cells.