Objective To discuss the clinical efficacy and potential mechanism of Yangyin Yifei Fang（ 养阴益肺方） in treating patients with chronic obstructive pulmonary disease（ COPD） in stable stage of Qi and Yin deficiency type. Methods Sixty-five patients with COPD in stable stage were randomized into a control group（ 33 cases） and a treatment group（ 32 cases）. The patients in both groups were given conventional treatment such as oxygen uptake and phlegm reducing

etc.

while the patients in the treatment group were additionally administered Yangyin Yifei Fang orally

with one dose each day. Both groups were treated for one month. The serum levels of leukotrience B4（ LTB4）

interleukin 8（ IL-8）

interleukin 17（ IL-17） and tumor necrosis factor α（ TNF-α） were observed before and after treatment

and correlation analysis was done. Also

Chinese medicine syndrome scores

modified dyspnea scale of English Medical Research Council（ m MRC）

6 minute walk test（ 6MWT） and lung function of both groups were compared before and after treatment

and clinical efficacy was evaluated. Results The overall response rates in the treatment group and the control group were respectively 87. 5% and 54. 6%

and the treatment group behaved better than the control group（ P < 0. 05）. After treatment

serum levels of LTB4

IL-8

IL-17 and TNF-α declined significantly in the treatment group（ P < 0. 05）

while in the control group

IL-8 and TNF-α did so（ P < 0. 05）.After treatment

the serum levels of LTB4

IL-17 and TNF-α in the treatment group were significantly lower than those in the control group（ P < 0. 05）. The correlation analysis showed that there were positive correlations between serum levels of LTB4 and IL-8

IL-17 as well as TNF-α before treatment in both groups（ P < 0. 05）; there was a positive correlation between LTB4 and IL-17 after treatment in the treatment group（ P < 0. 05）

and there was positive correlations between LTB4 and IL-17 as well as TNF-α both before and after treatment in the control group（ P < 0. 05）. In both groups

each item of Chinese medicine syndrome scores and m MRC score decreased significantly after treatment compared with those before treatment（ P < 0. 05）

while the scores of short breath

gasp and spontaneous perspiration in the treatment group were significantly lower than those in the control group（ P < 0. 05）. In the treatment group

6MWT and lung function after treatment improved compared with those before treatment

and they were significantly better than those in the control group（ P < 0. 05）. Conclusion Yangyin Yifei Fang shows good efficacy in treating COPD in stable stage of Qi and Yin deficiency type

and it could improve the clinical symptom. The potential mechanism may be blocking inflammatory cascade response and thus reducing the LTB4 level.