BACKGROUND: Increasing physical activity (PA) is considered to be an important factor for the efficient management of chronic obstructive pulmonary disease (COPD). Successful methods required to achieve improvements in PA following pulmonary rehabilitation (PR), however, are rarely reported. Therefore, we will conduct this trial to evaluate the effectiveness of using a COPD management program delivered to the patient via the KAIA COPD app, a mobile medical application, after the completion of PR. METHODS: This is the protocol for a randomized, controlled, open-label, multicentered trial that will be carried out at inpatient PR hospital centers in Germany and Switzerland. The interventions will involve the use of the KAIA COPD app program (Arm 1) or an active comparator, i.e., usual care (Arm 2). Patients completing an in-hospital PR program and consenting to participate in the study will be screened with the inclusion and exclusion criteria and enrolled in the study. After fulfilling the screening requirements, the patients will be randomized into one of the two arms with parallel group assignment in a 1:1 ratio. The training program will be delivered to the participants grouped in Arm 1 via the KAIA COPD app and to participants grouped in Arm 2 via the regular recommendations or standard of care by the PI. In total, 104 participants will be included in the trial. The treatment period will last for 24 weeks. Electronic versions of questionnaires will be used to collect patient-reported assessments remotely. The primary outcome measure is the change in physical activity of the intervention group in comparison to the control group, measured over 1 week as the mean steps per day with a Polar A 370 activity tracker, from baseline (end of PR) to the 6-month follow-up. The secondary outcome measures are functional exercise capacity, health status, sleep quality, exacerbation rate, and depression and anxiety symptoms assessed at several intervals. DISCUSSION: This study seeks to prove the effects of the KAIA COPD mobile application in COPD patients after PR. The app offers educational, exercise training plus activity monitoring and motivational programs that can be easily implemented in the patient's home setting, enabling patients to maintain the effects that are typically elicited in the short term after pulmonary rehabilitation for the long term. TRIAL REGISTRATION: German Clinical Trials Register ( DRKS00017275 ). Protocol version 2.0 dated 3 June 2019.