<b><i>Background:</i></b> The validity and reproducibility of the 6-minute stepper test (6MST) have already been demonstrated in patients with chronic obstructive pulmonary disease (COPD). <b><i>Objectives:</i></b> The aim of this study was to evaluate the responsiveness of the 6MST to pulmonary rehabilitation (PR) in patients with COPD, to determine a minimal important difference (MID) for the 6MST, and to compare the 6MST and the 6-minute walk test (6MWT). <b><i>Methods:</i></b> Sixty-two patients with COPD were included in a prospective experimental study. Participants underwent a 3-week inpatient PR program. The primary outcome was the change in the number of steps during the 6MST measured before and after PR. The secondary outcome included the change in the 6-minute walking distance (6MWD) pulse oximetry, heart rate, dyspnea, and leg discomfort during the tests measured before and after PR. MID was determined by anchor-based and distribution approaches. <b><i>Results:</i></b> After PR, we observed a significant increase in the number of steps during the 6MST (22.5 steps; 95% CI 13.8-31.3; p < 0.0001) and in the 6MWD (26.6 m; 95% CI 17.6-35.5; p < 0.0001). The 6MST and 6MWT were improved by 10.1 and 6.5%, respectively. The number of steps during the 6MST was significantly correlated with the 6MWD before (r = 0.72; p < 0.0001) and after PR (r = 0.66; p < 0.0001). MID was estimated to be around 20 steps. <b><i>Conclusion:</i></b> The 6MST appears to be as responsive as the 6MWT in assessing functional improvement during PR in patients with COPD. The 6MST is a low-cost assessment and requires limited space.