Abstract-In order to evaluate the efficacy of rehabilitation for persons with hemiplegia, a therapist usually makes judgment by directly observing posture changes, walking speed, activities not only in hospital, but also during daily living. Therefore, quantitative assessment of activities is most desirable. From this viewpoint, we have developed a device for ambulatory monitoring of posture changes, walking speed and activity scenario and evaluated its measurement accuracy by simultaneous recordings of a digital video camera. In order to investigate its applicability to a patient's activity monitoring, we have further developed a new monitoring system which can display static and dynamic motion pictures as well as detailed angle changes of the trunk, thigh and calf. This system makes a therapist to easily understand the patient's motion during training in rehabilitation center and activities during daily living. By evaluation on 6 patients with hemiplegia, the patients' motions were successfully monitored during walking in the rehabilitation center and daily living at their own home. The results clearly demonstrated that the system could detect detailed motion characteristics, indicating that the system appears useful for evaluating quantitatively the efficacy of rehabilitation.