Abstract: OBJECTIVE The current study was designed to evaluate the protective effects of baicalin on radiation-induced acute lung injury in mice. METHODS 50 ICR mice were divided into five groups randomly， namely， control group， X-ray group， X-ray+dexamethasone group (5mg/kg)， X-ray+baicalin group (20， 40 mg/kg)， with 8 in each group. Pathological changes in the lung tissues were observed. The ratio of lung wet/dry weight was also recorded. Besides， the level of neutrophil in bronchoalveolar lavage fluid (BALF) was detected to evaluate inflammatory cell infiltration. Moreover， the expressions of MDA， IL-6， TNF-α， p-NFκBp65 and p-IκBα， as well as the activity of SOD， were examined in lung. RESULTS Baicalin (20， 40 mg/kg) could effectively improve the radiation-induced lung pathological changes and reduce the number of inflammatory cells in BALF. The ratio of lung wet/dry weight was also decreased with the treatment of baicalin (20， 40 mg/kg). In addition， the activity of SOD was recovered and the end product of lipid peroxidation MDA was reduced meanwhile. The expressions of p-NFκBp65 and p-IκBα was extensively down-regulated with baicalin (20， 40 mg/kg) preconditioning， taking the expressions of NFκBp65 and IκBα as inner controls. CONCLUSION Baicalin could alleviate radiation-induced acute lung injury due to its antioxidant and anti-inflammatory properties.