We hypothesize that add-on Rhodiola L extract capsule to the regimen of patients with moderate-to-severe COPD (1) may provide a potential of systemic effects of anti-inflammation and anti-oxidation for these patients, and these effects (2) may reflect in the improvement of patients' physiological measurements, quality of life and exercise tolerance.

This is a single center, randomized, double-blind, placebo controlled clinical trial.

Eligibility criteria:

1. moderate-to-severe COPD patients
2. aged 40-80 years,
3. abstaining from cigarette smoking or maintaining a stable dose of cigarette consumption,
4. no acute exacerbation of COPD,
5. clinically being stable for one month and longer,
6. not undergoing exercise training program.

Primary endpoint:

six-minute walk distance in meters at week 12.

Inclusion Criteria:

1. moderate-to-severe COPD patients
2. aged 40-80 years,
3. abstaining from cigarette smoking or maintaining a stable dose of cigarette consumption,
4. no acute exacerbation of COPD,
5. clinically being stable for one month and longer,
6. not undergoing exercise training program.

Exclusion Criteria:

1. uncontrolled diabetes mellitus by plasma fasting sugar >200 mg/dl,
2. uremia or CKD stage 5,
3. chronic heart failureby NYFC III,
4. cerebrovascular disease,
5. uncontrolled anemia by Hb < 10 mg/dl,
6. active malignant diseases,
7. other hospitalized acute illness,
8. systemic prednisolone > 10 mg per day.