Objective：To observe the dynamic changes of plasma high-mobility group box 1（HMGB1） and tumor necrosis factor-α （TNF-α） in patients with severe blunt chest trauma，to assess the severity of injury and to predict its prognostic value. Methods：A total of 57 consecutive blunt chest trauma patients with an abbreviated injury scale≥3 from March 2011 to December 2011 were included and blood samples were taken from patients every other day from d1 to d7 after admission. Plasma concentration of HMGB1 and TNF-α were measured by a quantitative ELISA. Development of post-traumatic complications was observed and their relations with plasma levels of HMGB1 and TNF-α were analyzed. Results：Patients’ median age was （44.5±12.6） years and the median in－jury severity score（ISS） was （18.4±6.02）. Both the plasma levels of HMGB1 and TNF-α had positive correlation with ISS（d1：r=0.29，P=0.068 vs. r=0.507，P=0.016；d3：r=0.578，P<0.001 vs. r=0.411，P=0.021；d5：r=0.645，P<0.001 vs. r=0.365，P=0.07；d7：r=0.683，P<0.001 vs. r=0.321，P=0.019）. There were significantly increases in mean plasma HMGB1 levels on d3，5，7 in patients with ISS≥20 compared with those with ISS<20（all P<0.05）. Plasma levels of HMGB1 showed a higher sensitivity but less specificity than TNF-α in prediction of complications occurrence（P<0.05）. Conclusions：Plasma levels of HMGB1 seem to be most suitable for severity assessment and prediction of post-traumatic complications occurrence in patients with severe blunt chest trauma.