To study the effect of capsaicin on the oxidative stress in acute lung injury induced by endotoxin in mice.Methods:A total of 120 BALB/c mice were randomized into control group(n=30)，capsaicin group(n=30)，endotoxin group(acute lung injury group)(n=30)，and capsaicin+endotoxin group(n=30).They were killed at 2，4 and 6 h after anesthesia，respectively，and lung tissue samples were collected.The level of malondialdehyde(MDA) was determined by chemical colorimetry and level of nitrogen oxides(NOX) by nitric oxide(NO) reductase method.Levels of tumor necrosis factor-α(TNF-α) and interleukin-1β(IL-1β) in lung tissues of mice were detected by enzyme-linked immunosorbent assay(ELISA).Pathological changes of lung tissue were observed based on hematoxylin and eosin(HE) staining.Results:The levels of MDA，NOx，TNF-α，and IL-1β in the lung tissue of mice in the endotoxin group were increased compared with those in the control group(P<0.05)，but the levels in the capsaicin group showed no significant changes compared with those in the control group(P>0.05).Levels of MDA，NOx，TNF-α，and IL-1β in the lung tissue of mice in the capsaicin+endotoxin group were lower than those in the endotoxin group(P<0.05).Under light microscope，the lung tissue damage in endotoxin group was more obvious than that in control group at 4 h and 6 h，and capsaicin group showed no significant variation.In addition，the damage in the capsaicin+endotoxin group was milder than that in endotoxin group.Conclusion:Oxidative stress is an important link in the development of acute lung injury in endotoxemia mice.Capsaicin can alleviate oxidative stress injury in acute lung injury mice by reducing levels of superoxide dismutase(SOD)，NOX，TNF-α，and IL-1β.