Background Along with an aging population, the field of robot technology in rehabilitation is expanding. As new technologies develop, it is important to test these clinically before implementation. To assess the possibilities of undertaking a future randomized controlled trial (RCT), the aim of this study was to pilot test and investigate the feasibility of a newly developed passive mobilization robot device in geriatric medicine patients. Methods We used a robot to perform passive mobilization for all recruited patients while they were lying in bed. Inclusion criteria include the following: ≥ 65 years of age, able to walk before hospitalization, and not capable of walking > 2 m at the first day of hospitalization. Exclusion criteria include the following: known moderate/severe dementia, unstable fractures (back, pelvis, or legs), high intracranial pressure, pressure ulcers/risk of developing pressure ulcers due to fragile skin, positive Confusion and Assessment Method (CAM) score, not able to understand Danish, and medical instability. A mixed-methods approach, including structured interviews for patients and relatives, questionnaires and semi-structured interviews for the staff, and observations in the clinic were used as data collection methods. A 6-week pilot test preceded the feasibility study to test study design, safety, interview guide, and setting, and to become familiar with the robot. Results The pilot test included 13 patients, made the staff confident in the use of the robot, and led to the correction of the interview guide. In the feasibility study, 177 patients were screened, 14 patients (four men, nine women) included, and 13 completed the intervention (median [IQR] age 86 [82–92] years). Overall, the robot was easy to use during passive mobilization and fully accepted by patients and relatives. Staff, however, found the robot difficult to maneuver. No adverse events were reported. Conclusions Use of robot technology in passive mobilization of older patients was feasible and well accepted by patients, relatives, and staff. Technical and workflow-related issues, as well as the robot not performing active mobilization, affects the launch of a RCT and thereby its implementation in geriatric medicine patients.