Objective To observe the dynamic changes of high mobility group protein B1 ( HMGB1 )expression in the lung of rats with Vibrio vulnificus sepsis so as to unravel the role of HMGB1 in lung injury.Methods Sixty rats of clean grade were randomly divided into normal control group ( A group, n = 10) and Vibrio vulnificus sepsis group (B group, n =50). Sepsis model was made in rats with subcutaneous injection of Vibrio vulnificus with concentration of 6 × 108 cfu/ml in dose of 0. 1 ml/100 g into left lower limb.The rats of group B were sacrificed 1 h, 6 h, 12 h, 24 h and 48 h after infection for taking lung tissues to detect the water content of lung and to observe the histopathological changes in lung under light microscope.The expression of HMGB1 mRNA and the level of HMGB1 protein in the lungs were detected by RT-PCR and Western blot, respectively. Data were analysed with ANOVA and LSD method for comparison between groups, and P ＜0.05 was considered statistically significant. Results Compared with the group A (0.652±0. 177), the expressions of HMGB1 mRNA in lung of rats of group B were significantly higher in 12 hours (1. 161 ±0.358, P=0.013), 24 hours (1.679 ±0.235, P =0.000) and 48 hours (1.258 ±0.274, P=0.004) and reached the peak in 24 h. Compared with group A (0.594 ±0. 190), the level of HMGB1 protein in rats of group B 6 h after infection ( 1. 408 ± 0. 567, P = 0. 026) was significantly increased (P＜0.05), and it reached peak in 24 h (2.415 ± 1.064, P =0.000) after infection. Compared with group A (0.699 ± 0.054), the lung water contents in rats of group B were significantly increased in 6 h (0.759±0.030, P=0.001), in 12 h (0.767 ±0.023, P =0.000), in 24 h (0.771 ±0.043, P=0.000) and in 48 h (0.789 ±0.137, P=0.000) after infection. Compared with group A, the pathological changes in the lung of rats in group B showed clearly marked pulmonary vascular congestion, interstitial edema and inflammatory cell infiltration, and those changes became more and more serious until alveolar sacs entirely collapsed and the boundaries of the alveolar septa could not be clearly identified in 48 h. Conclusions Vibrio vulnificus sepsis leads to the lung injury of infected rats, and the increase in the expression of HMGB1 mRNA in lung might be one of the mechanisms of lung injury in rats with Vibrio vulnificus sepsis.