Joints mobilization is an essential but subjective treatment in the physical therapy of the patients with joint hypomobility such as frozen shoulder. Recently many instrumented force and displacement indentations have been proposed for assessing and diagnosis of joints stiffness. The devices are not, however, feasible and applicable for use in clinical and therapeutic conditions considering the requirements of the joints mobilization principles in physiotherapy. This paper describes a novel design of a robotic system for mobilization of glenohumeral joint and the preliminary evaluation of mobilization robot in a subject with hypomobile glenohumeral joint. A new mechanism is presented which enables the robotic system to execute the mobilization maneuver in 1 inch linear motion path when it grasps the glenohumeral joint and holds the upper limb situated in the 90 degrees relaxed abduction. It was shown that the mobilization robot can be used effectively and practical for mobilization treatment. Furthermore such a device may be used as a diagnostic and assessing device for evaluating the stage of hypomobility based on Maitland method.