Purpose: A high body mass index (BMI) provides an advantage for survival in patients with chronic obstructive pulmonary disease (COPD). The aim of this study was to investigate the effects of obesity on respiratory muscle strength, exercise capacity, and physical activity level in patients with COPD. Materials and Methods: Twenty-eight male COPD patients (age: 63.07±6.32 years, FEV1: 36.9±11.0%) participated in this study. The subjects were divided into two groups as overweight/obese (25≤BMI≤34.9 kg/m 2, n=14) and normal (18.5≤BMI≤24.9 kg/m2, n=14). Pulmonary function testing and six-minute walk test were performed. Respiratory muscle strength was evaluated using a portable mouth pressure device. Physical activity level of the subjects was determined using an accelerometer. Results: Airway obstruction level was similar in both groups (p>0.05). Overweight/obese COPD patients' inspiratory muscle strength (94.57±18.72 cmH2O), expiratory muscle strength (155.07±42.86 cmH 2O), and physical activity level (319.3 kcal/day) were statistically higher than patients with a normal BMI (inspiratory muscle strength: 79.64±26.14 cmH2O, expiratory muscle strength: 124.36±23.70 cmH2O, and physical activity level: 275.9 kcal/days, p<0.05). There was no significant difference in 6-minute walk distance between both groups, however work done during the test was significantly higher in overweight/obes group (3037.0±8662.91 kg/m ve 4240.3±10372.59 kg/m, p<0.05). Conclusion: Being overweight or obese preserves respiratory muscle strength in COPD. Although physical activity level of obese/overweight patients was higher than those of normal weight group, both groups had an insufficient physical activity levels. The clinical condition caused by being overweight or obese patients with COPD can provide a better prognosis.