Exoskeleton robots can facilitate rehabilitation of patients with upper or lower limb disabilities. To make exoskeletons more friendly and accessible to patients, they need to be lightweight and compact without compromising major performances. Existing upper-limb exoskeletons focus on the shoulder and the upper arm while the fine-motion rehabilitation of the forearm is often ignored. This paper presents an elbow-wrist exoskeleton with five degrees-of-freedom. Using a 5R spherical mechanism for the wrist module and a slider crank mechanism for the elbow module, this exoskeleton can provide the complete motion assistance for the forearm. This exoskeleton with optimized dimensions can produce large torque and motion output while the motors are placed parallel to the forearm and the elbow joint. Thus better inertia properties can be achieved while lightweight and compactness are maintained. Series elastic actuators (SEAs) are proposed to obtain accurate force and impedance control at the exoskeleton-forearm interface. We expect that this rehabilitation exoskeleton can be used alone or in conjunction with other exoskeleton robots to provide a means of robot-aided upper limb rehabilitation.