Background: Self-efficacy explores the emotional functioning and coping skills of an individual and is thought to be a strong predictor of health behaviors, which is particularly important for pulmonary rehabilitation (PR). However, to our knowledge, there is no measure of self-efficacy developed to explore behavior change in the context of PR. Methods: We investigated the reproducibility and sensitivity of Pulmonary Rehabilitation Adapted Index of Self-Efficacy (PRAISE): a tool adapted from the General Self-Efficacy Scale (GSES) to measure the dimension of self-efficacy at the time of a course of PR. Twenty-nine clinically stable patients with COPD completed PRAISE on their initial assessment to PR. The tool was then completed 7 days later. An additional 225 patients completed PRAISE prior to, and on completion of a 7-week course of PR. In addition, exercise capacity was measured by the incremental shuttle walk test (ISWT), with the Medical Research Council (MRC) dyspnea scale, Chronic Respiratory Questionnaire-Self Reported (CRQ-SR), and Hospital Anxiety and Depression Scale (HADS) also being collected. This process was repeated postrehabilitation. Data were then analyzed to investigate the possibility that PRAISE could be an indicator of PR response. Results: In the reproducibility study, the mean change in score was 0.72 (95% CI, −2.27-0.82), examined with intraclass correlation coefficients, r = 0.99; indicating PRAISE test-retest reproducibility. The mean change of score in the sensitivity study pre- to post-PR was 3.59 (95% CI, 2.24-4.73; P = .015). Change in the ISWT was 83.44 m (95% CI, 54.0-112.8; P <.0001). There were several statistically significant differences between variables, particularly with the mastery and emotion elements of the CRQ-SR at baseline, but this was lost post-PR. This observation was also found with HADS. No significant differences were found between MRC dypsnea scale grades with the change in PRAISE score. PRAISE could not predict a successful outcome of PR. Conclusions: The PRAISE tool is a reliable and sensitive measure of self-efficacy for patients with COPD attending PR. .