PURPOSE: To determine whether an early rehabilitation program was safe and feasible for patients during an acute exacerbation of chronic obstructive pulmonary disease (COPD). METHODS: In this phase 1 randomized controlled trial, patients with an acute exacerbation of COPD admitted to the hospital were randomly allocated to a low-intensity exercise group, a moderate- to high-intensity exercise group, or a control group, who received routine physical therapy. In addition to routine physical therapy, patients in the exercise group had to participate in an exercise program. The program consisted of twice-daily aerobic and resistance exercise sessions. Primary outcomes were the number and classification of adverse events and program adherence. RESULTS: In 174 exercise sessions, there was 1 serious adverse event of arrhythmia in the low-intensity exercise group that resolved within 1 hour. There were 12 other minor adverse events involving 5 patients with no significant differences between groups. Patients completed an average of 80% of their scheduled sessions with no significant between-group differences. The exercise groups improved significantly in walking distance; however, no significant between-group differences were observed. CONCLUSIONS: There was preliminary evidence that it was safe and feasible to implement an exercise program for patients during an acute exacerbation of COPD. Additional studies with larger sample sizes are required to accurately evaluate program effectiveness.