Objective To investigate the effect of recombinant BPI on the inflammatory response and TLR4 / NF- κB signaling pathway in mice infected with Mycoplasma pneumoniae. Methods BALB/ c mice ( n= 67) were randomly divided into the control group, M. pneumoniae (MP) model group and high-, medium- and low-dose groups of recombinant BPI protein. The MP model was established by nasal drip of 1×10⁶ CCU/ mL (100 μL) MP bacteria solution for 4 days. After successful modeling, mice in each treatment group were injected with 1. 5 mL of recombinant BPI protein solution with concentrations of 0. 45,0. 3 or 0. 15 mol / L through the lumbar vein. Mice in the control group and model group were injected with the same amount of normal saline through the lumbar vein. All mice were treated for 4 weeks. The lung tissue and serum of mice was collected at the last administration, and the lung index and dry wet ratio were calculated; the pathological changes of lung tissue were observed by HE staining method and the pathological score of lung tissue was determined. Serum inflammatory factors were detected by ELISA and the mRNA expressions in lung tissue were detected by RT-PCR; Western blot was used to detect the expression of TNF-α, IL-6 and IL-1β. Results Compared with the MP model group, the BPI protein group showed a decreased lung index (P<0. 05), increased dry wet ratio (P<0. 05), and decreased serum levels of TNF-α, IL-1β and IL-6 (P<0. 05). Compared with MP model group, the mRNA and protein expressions of TLR4 and NF-κB p65 in lung tissue of mice in recombinant BPI group were significantly down-regulated (P<0. 05), and the mRNA and protein expressions of I-κBα were significantly up-regulated ( P< 0. 05). Conclusions Recombinant BPI protein may inhibit the production of TNF-α, IL-1β and IL-6 by regulating the TLR/ NF-κB signaling pathway, so as to reduce the pulmonary inflammatory response in mice.