Objective : The object of this study was to observe the effects of Lonicerae Flos (LF) aqueous extracts on lipopolysaccharide (LPS)-induced rat acute lung injury. Method : Five different dosages of LF extracts were orally administered once a day for 28 days before LPS treatments, and then all rats were sacrificed after 5 hour-treatment of LPS. Eight groups of 16 rats each were used in the present study. The following parameters caused by LPS treatment were observed ; body weights, lung weights, pulmonary transcapillary albumin transit, arterial gas parameters (pH, $PaO_2$ and $PaCO_2$) bronchoalveolar lavage fluid (BALF) protein lactate dehydrogenase (LDH), and proinflammatory cytokines tumor necrosis factor-${alpha}$ (TNF-${alpha}$), interleukin-$1{eta}$ (IL-$1{eta}$) contents, total cell numbers, neutrophil and alveolar macrophage ratios, lung malondialdehyde (MDA), myeloperoxidase (MPO), proinflammatory cytokines TNF-${alpha}$ and IL-$1{eta}$ contents. In addition, the histopathologic changes were observed in the lung in terms of luminal surface of alveolus, thickness of alveolar septum, number of polymorphonuclear neutrophils. Result : As results of LPS-injection, dramatical increases in lung weights, pulmonary transcapillary albumin transit increases, increases in $PaCO_2$, decreases in pH of arterial blood and $PaO_2$, increases of BALF protein, LDH, TNF-${alpha}$ and IL-$1{eta}$ contents, total cells, neutrophil and alveolar macrophage ratios, TNF-${alpha}$ and IL-$1{eta}$ contents increases were detected with decreases in LSA and increases of alveolar septum and PMNs numbers, respectively as compared with intact control. These are means that acute lung injuries (resembling acute respiratory distress syndrome) are induced by treatment of LPS mediated by inflammatory responses, oxidative stress and related lipid peroxidation in the present study. However, these LPS-induced acute lung injuries were inhibited by 28 days continuous pretreatment of 250 and 500mg/kg of LF extracts. Because of lower three dosages of LF treated groups, 31.25 and 62.5 and 125mg/kg did not showed any favorable effects as compared with LPS control, the effective dosages of LF in LPS-induced acute lung injuries in the present study, is considered as about 125mg/kg. The effects of 250mg/kg of LF extracts showed almost similar effects with ${alpha}$-lipoic acid 60mg/kg in preventing LPS-induced acute lung injuries. Conclusion : It seems that LF play a role in protecting the acute respiratory distress syndrome caused by LPS.