Abstract： Objective To investigate the role of p38 MAPK pathway in the expression of high mobility group box 1 (HMGB1) in lung tissue in a rat model of ventilator-induced lung injury. Method Twenty-fonr healthy Sprague Dawley (SD) rats were randomly divided into 3 groups (n = 8 each) : group A, spontaneous breathing; group B, small tidal volume ventilation (Vt = 8 mL/kg) and group C, high tidal volume ventilation (Vt = 40 mL/kg). 1he animals in group B and C were mechanically ventilated for 4 hours and all animals were sacri-riced. The lungs were removed for: (1) lung lavage and determination of total protein contnt and WBC and neu-trophil counts in broncho-alveolar lavage fluid (BALF) ; (2) determination of W/D lung weight ratio and myelop-erexidnse (MPO) activity; (3) detennination of HMGB1 protein and mRNA expression and p38 MAPK activity in lung tissue. Differences within the groups were analyzed using One way ANOVA. Results The inflammatory re-sponse as evidenced by total protein (1.77 ± 0.68) g/L and WBC (106.55 ± 28.17) × 10~7/L in BALF, W/D lung weight ratio (7.16±1.02) and MPO activity (3.94±1.21) U/g were significantly higher in group C com-pared with group A (P <0.05); HMGB1 protein (0.64±0.17) and mRNA (1.17±0.45) expression and p38 activity (0.51±0.12) also significantly increased in group C (P <0.05). Of the above indexes, there were no statistical differences between group B and group A (P > 0.05). Conclusions High tidal volume ventilation in-daces acute lung injury, which may be related with upregulation of HMGB1 expression through p38 MAPK signal pathway.