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Acute lung injury (ALI) is a common emergency and severe case in clinic. High mobility group protein box 1 (HMGB1) can be treated as a new anti-inflammatory treatment target. Toll-like receptor 4 (TLR4) is an important receptor of HMGB1. Ketamine is a widely used intravenous anesthetic with good anti-inflammatory and immune regulating function. Whether it can protect ALI through inhibiting HMGB1 and TLR4 expression in lung tissue still needs further investigation. Male SD rats were randomly divided into control, lipopolysaccharide (LPS) group and ketamine intervention group with 15 rats in each group. The rats were euthanatized at 24 h after modeling and the bronchoalveolar lavage fluid (BALF) was collected for HMGB1 and TLR4 level detection. Western Blot was applied to analyze HMGB1 and TLR4 protein expression in the lung tissue. HMGB1 and TLR4 concentration in BALF were 5.369 ± 1.564 ng/ml and 43.980 ± 7.524 pg/ml in the control, respectively. They were 12.358 ± 4.681 ng/ml and 102.538 ± 8.412 pg/ml in LPS group, and 7.399 ± 2.346 ng/ml and 87.208 ± 7.558 pg/ml in ketamine intervention group, respectively. Their levels increased significantly in LPS group and down-regulated after ketamine intervention. HMGB1 and TLR4 protein expression in lung tissue elevated obviously in LPS group, and decreased after ketamine treatment. HMGB1 and TLR4 protein level showed positive correlation in lung tissue (r = 0.921, P < 0.001). Ketamine can inhibit HMGB1 and TLR4 expression in ALI, and alleviate LPS induced rat lung injury.