To determine the influence of “thin”, “normal”, and “obesity” on the motor function and exercise capacity of chronic obstructive pulmonary disease (COPD) patients, as well as whether “obesity” is actually “harmful” for such patients. A total of 103 COPD patients in a stable condition were classified into three groups: a “thin group” (BMI<18.5), an “normal group” (18.5≤BMI<25), and an “obesity group” (BMI≥25). Fourteen patients from each group matched for %FEV_1.0, sex, and age were evaluated. The measurement items were: respiratory function, respiratory muscle strength, lower and upper limb muscle strength, the 30-sec chair-stand test (CS-30), timed up and go test (TUG), 6-minute walking test (6MWT), incremental shuttle walking test (ISWT), Nagasaki university respiratory questionnaire (NRADL), and St. George’s respiratory questionnaire (SGRQ). As a result of comparing the three groups, the %MIP was significantly higher in the obesity compared to thin group (p=0.04). No differences were seen between the groups in the mMRC, %MEP, quadriceps femoris muscle strength (%), CS-30, TUG, 6MWT, ISWT, NRSDL, and SGRQ, but these values showed a tendency to be favorable in the obesity group. The BMI was significantly and positively correlated with the %MIP and NRADL. It was suggested that management of the respiratory muscle strength, exercise tolerance, and ADL when COPD patients are obese rather than thin can be possibly associated with a higher QOL.