Abstract: Objective：To investigate the correlationship between peripheral CD25+Foxp3+Treg and Th17 cellmediated immune imbalance and the progression of chronic obstructive pulmonary disease (COPD). Methods：A total of sixtynine patients with COPD in stable stage or acute exacerbation of COPD were recruited from Shanghai Fifth People’s Hospital of Fudan University from January 2012 to March 2015. At the same time, the nonsmokers and smokers with normal lung function, each 20 cases, were also used as the healthy controls. The pulmonary function of all subjects was evaluated. The percentages of Th17 and CD25+Foxp3+Treg cells in CD4+ cells from peripheral blood were determined by flow cytometry. The changes of Th17/CD4+, CD25+Foxp3+Treg/CD4+ and Th17/CD25+Foxp3+Treg ratios in the different groups and their clinical significance were analyzed. Results：Compared with the healthy control group, the ratios of Th17/CD4+ and Th17/CD25+Foxp3+Treg in peripheral blood of patients with stable COPD were significantly increased (P＜0.05), while the ratio of CD25+Foxp3+Treg/CD4+ was significantly decreased (P＜0.05). The ratios of Th17/CD4+, CD25+Foxp3+Treg/CD4+ and Th17/CD25+Foxp3+Treg in patients with acute exacerbation of COPD were all increased as compared with the healthy control (all P＜0.05). With the decline of lung function, the ratios of Th17/CD4+ and Th17/CD25+Foxp3+Treg were gradually upregulated in patients with mild, moderate, severe, very severe COPD (P＜0.05), while the ratio of CD25+Foxp3+Treg/CD4+ was gradually downregulated (P＜0.05). Moreover, the ratios of Th17/CD4+ and Th17/CD25+Foxp3+Treg in COPD patients were negatively correlated with lung function (P＜0.05), while the ratio of CD25+Foxp3+Treg/CD4+ was positively correlated with lung function (P＜0.05). Conclusions：Th17/CD25+Foxp3+Treg imbalance involves in the progression of COPD, suggesting that Th17/CD25+Foxp3+Treg immunomodulatory therapy may become a new approach for the treatment of COPD.