Today, obesity is a global health problem and can lead to serious health complications. Bariatric surgery is recognized as an effective treatment option to achieve long-term weight loss and health improvement in overweight or obese individuals. However, appropriate tools are needed to assess the physical activity levels of patients before and after bariatric surgery and to guide rehabilitation processes after surgery. The Duke Activity Index (DAI) is a scale used to assess activities of daily living and was developed at Duke University Medical Center. The DAI has been widely used to determine patients' physical functioning and monitor their activity levels in various health conditions and post-surgical recovery processes. The aim of this study was to evaluate the psychometric properties of the DAI and to examine whether it is an effective tool for determining physical activity levels in patients who are candidates for bariatric surgery.