Summary Although obesity is a common co-morbid condition in COPD, relatively little is known how it may affect functional exercise capacity. Accordingly, we compared physiologic responses during a 6 min walk test in 10 obese and 10 non-obese COPD patients matched by gender, age, and spirometric severity category. Patients first exercised on a treadmill to determine maximal exercise responses, then following a rest period they completed a 6 min walk test. Breath by-breath analyses of expired air via a facemask was obtained using a portable, battery operated device. Oxygen consumption (VO2), carbon dioxide production (VCO2), tidal volume (VT), respiratory rate (RR), minute ventilation (VE), and inspiratory capacity (IC) were compared. The mean FEV1 in the obese and non-obese groups was 52 ± 13 and 58 ± 18 percent of predicted, respectively, and the BMI of the obese patients was 37 ± 02 kg/m2. Obese patients had shorter 6 min walk distances than non-obese patients (247 ± 73 vs 348 ± 51 m, respectively, p = 0.003), but walk-work, defined as 6 min walk distance × weight (in kg), was not different. There were no significant between-group differences in any exercise variable measured during the 6 min walk test. In both groups, VO2 and VE increased linearly over the first 2–3 min, then plateaued at approximately 80% of maximum. Although 6 min walk distance is shorter in obese COPD patients, their physiologic responses are similar to those of non-obese patients.