Chronic obstructive pulmonary disease (COPD) is a disease that continues to generate a great deal of research and this research must continue, both because it is not completely curable and because of the large patient population. The importance and benefits of exercise training in COPD patients are clear. One of the most preferred types of exercise training is the so-called aerobic exercise training, which typically takes the form of walking. A typical walking training does not use a slope or may include an uphill slope. However, recently there have been publications about downhill walking and its benefits in COPD. Walking on a level, uphill, and downhill slope may have the potential to result in different gains by using different muscle groups more. Therefore, this study aimed to compare the effects of walking training on exercise capacity, respiratory functions, muscle strength, and functional status in COPD patients with three different slope types: level, uphill, and downhill.