ObjectiveTo investigate the role and mechanism of S100A8/A9 in rat model of chronic obstructive pulmonary disease (COPD). Methods Twelve Wistar rats were randomly divided into a normal control group and a COPD group. The COPD model was established by exposing the rats to cigarette smoke and injected lipopolysaccharide (LPS) in bronchus for 1 month. The pathological changes of the lung tissue were observed under light microscope, and the emphysema indexes of pulmonary mean linear intercept (MLI), mean alveolar numbers (MAN) and pulmonary alveolar area (PAA) were analyzed by image analysis system. The concentrations of S100A8/A9 in serum and bronchoalveolar lavage fluid (BALF) were measured by enzyme linked immunosorbent assay. The mRNA expression levels of S100A8, S100A9, Toll-like receptor-4 (TLR4) and myeloid differentiation factor 88 (MyD88) of lung tissues were measured by real time polymerase chain reaction. The protein expressions of S100A8/A9, TLR4 and MyD88 of lung tissues were detected by immunohistochemistry. Results After cigarette smoking and LPS injection for 1 month, the rat lung tissue appeared in accordance with the typical pathological changes of COPD. The MLI, MAN and PAA had obvious difference compared with the normal control group (P<0.05). The concentrations of S100A8/A9 protein in BALF and serum of the COPD group were obviously higher than those of the normal control group (P<0.05). The levels of S100A8, S100A9, TLR4 and MyD88 mRNA of lung tissues in the COPD group were obviously higher than those in the normal control group (P<0.05), and the expression levels of S100A8 and S100A9 mRNA were positively correlated with the expression levels of TLR4 and MyD88 mRNA respectively (P<0.05). The levels of S100A8/A9, TLR4 and MyD88 protein of lung tissues in COPD group were obviously higher than those in normal control group (P<0.05), and the levels of S100A8/A9 protein were positively correlated with the levels of MyD88 and TLR4 protein (P<0.05). Conclusions As a new inflammatory mediator, S100A8/A9 may be involved in the occurrence and development of COPD. By up-regulating the expression of TLR4 and MyD88, the classical TLR4-MyD88 inflammatory pathway is activated, thus promotes the occurrence and development of COPD.