OBJECTIVE To study the correlations between lung function and Th1/Th2 polarization, signal transducer and activator of transcription (STAT) proteins in rats of chronic obstructive pulmonary disease (COPD). METHODS Sixty rats were randomly divided into normal control group, sham group and model group. The COPD rat models were developed by lipopolysaccharide (LPS). The changes of pulmonary function were detected at 28 d after modeling. The lung tissues of rats were observed by HE staining, and serum IFN-γ, IL-4, IL-12, and IL-13 were determined by ELISA. The mRNA expressions of IFN-γ and IL-4 were examined by PCR, and STAT4, STAT6 proteins in lung tissues were detected by Western blotting. RESULTS Inflammation of lung tissues was more serious, the levels of serum IFN-γ, IL-12 and Th1/Th2, IFN-γ mRNA and STAT4 protein in lung tissues were higher, and lung function, the levels of serum IL-4 and IL-13, IL-4 mRNA and STAT6 protein in lung tissues were lower in model group than those in normal control and sham groups (P < 0.05 or P < 0.01). Correlation analysis showed that there were negative correlations between pulmonary function parameters and IFN-γ, Th1/Th2, STAT4 protein, and positive correlations between pulmonary function parameters and IL-4, IL-13, IL-4 mRNA, STAT6 protein (P < 0.01 or P < 0.05). CONCLUSION The reduced lung function was found related to airway inflammation, cell Th1/Th2 imbalance in COPD. STAT4 and STAT6 involve in the regulation of Th1/Th2 cells. All of the above factors lead to the occurrence of COPD in rats.