Robots for surgery and rehabilitation have emerged and are gaining popularity among patients and medical doctors with their obvious benefits, such as overcoming obstacles from human users’ physical restraints, reducing physicians’ workload, and enhancing the efficacy of medical treatment. The development of medical robots meets two challenges related to their special application environments, including sterilization hazards and size/weight limitation. Medical robots (e.g., surgical robots) usually need to have close contact with human skin or organs, which need to be sterilized. However, chemical or heat sterilization on the robots poses an inevitable risk of damage on the motors, sensors, and other electronic components. The size of the surgical robot needs to be compact to gain access to surgical sites. The rehabilitation robots that patients wear have to limit their size and weight. Wire-driven actuation is a potential solution to solve these issues by avoiding the use of bulky mechanical gears and links and locating the electronic components far away from the sterilization environment. This paper presents the development of a novel wire-driven universal joint for medical robot design. With its special structure, this robotic joint has self-decoupled kinematics which can simplify its control system and increase motion accuracy. Benchtop experiments are conducted to verify the functionality of this joint and the effectiveness of its self-decoupled kinematics.