Abstract: OBJECTIVE To explore the role of high mobility group protein B1（HMGB1）/Toll-like receptor 4（TLR4） signaling pathway in ventilator-associated pneumonia（VAP） in rats. METHODS Totally 72 rats were randomly divided into the autonomous respiration blank control group（the group C）, the normal tidal volume mechanical ventilation group（ the group V） and the high tidal volume mechanical ventilation group（the HV group）, with 24 rats in each group. The group C was not treated with mechanical ventilation, the group V was given normal tidal volume mechanical ventilation, and the HV group was treated with high tidal volume mechanical ventilation. The total protein, inflammatory factors interleukin-6（IL-6）, interleukin-10（IL-10）, tumor necrosis factor-α（TNF-α）, macrophage inflammatory protein-2（MIP-2） and myeloperoxidase（MPO） in bronchoalveolar lavage fluid（BALF） as well as wet/dry weight（W/D） of lung tissues, expression quantities of HMGB1 and TLR4 mRNA and protein in lung tissues were detected. RESULTS The W/D and pathological scores of lung tissues of the group V and the group HV were significantly higher than those of the group C（P＜0.05）; the levels of BALF total protein, IL-6, IL-10, TNF-α, MIP-2 and MPO of the group V and the group HV were significantly higher than those of the group C（P＜0.05）; the expression quantities of HMGB1 and TLR4 mRNA and protein in lung tissues were significantly higher in the group V and the group HV than in the group C（P＜0.05）. CONCLUSION HMGB1 and TLR4 are closely related to various types of inflammatory mediators. The mechanism of VAP may be related to the HMGB1/TLR4 signaling pathway.