Background : It is known that pulmonary rehabilitation improves dyspnea and exercise tolerance in patient with chronic lung disease, although it does not improve pulmonary function. But there is a controversy whether this improvement after pulmonary rehabilitation is due to increased aerobic exercise capacity. We performed this study to evaluate the effect of pulmonary rehabilitation for 6 weeks on the pulmonary function, gas exchange, exercise tolerance and aerobic exercise capacity in patients with chronic lung disease. Methods : Pulmonary rehabilitations including education, muscle strengthening exercise and symptom-Umited aerobic exercise for six weeks, were performed in fourteen patients with chronic lung disease (COPD 11, bronchiectasis 1, IPF 1, sarcoidosis 1 ; mean age $57{pm}4$ years; male 12, female 2). Pre- and post-rehabilitaion pulmonary function and exercise capacity were compared. Results: 1) Before the rehabilitation, FVC, $FEV_1$ and $FEF_{25-75%}$ of the patients were $71.5{pm}6.4%$. $40.6{pm}3.4%$ and $19.3{pm}3.8%$ of predicted value respectively. TLC, FRC and RV were $130.3{pm}9.3%$, $157.3{pm}13.2%$ and $211.1{pm}23.9%$ predicted respectively. Diffusing capacity and MVV were $59.1{pm}1.1%$ and $48.6{pm}6.2%$. These pulmonary functions did not change after pulmonary rehabilitation. 2) In the incremental exercise test using bicycle ergometer, maximum work rale ($57.7{pm}4.9$) watts vs. $64.8{pm}6.0$ watts, P=0.036), maximum oxygen consumption ($0.81{pm}0.07$ L/min vs. $0.96{mu}0.08$ L/min, P=0.009) and anaerobic threshold ($0.60{pm}0.06$ L/min vs. $0.76{mu}0.06$ L/min, P=0.009) were significantly increased after pulmonary rehabilitation. There was no improvement in gas exchange after rehabilitation. 3) Exercise endurances of upper ($4.5{pm}0.7$ joule vs. $14.8{pm}2.4$ joule, P<0.001) and lower extremity ($25.4{pm}5.7$ joule vs. $42.6{pm}7.7$ joule, P<0.001), and 6 minute walking distance ($392{pm}35$ meter vs. $459{pm}33$ meter, P<0.001) were significantly increased after rehabilitation. Maximum inspiratory pressure was also increased after rehabilitation ($68.5{pm}5.4$ $CmH_2O$ VS. $80.4{pm}6.4$ $CmH_2O$, P<0.001). Conclusion: The pulmonary rehabilitation for 6 weeks can improve exercise performance in patients with chronic lung disease.