A split belt treadmill robot for gait rehabilitation was developed to improve the symmetry of the stance phase time of patients with stroke. The system, which increases the stance phase time of the affected leg and then realizes a well-balanced gait, is divided into two components. First, the stance phase of the unaffected ("sound") and affected legs is measured and presented visually in real time to the patient and physical therapist as biofeedback. Second, using the biofeedback of the stance phase, the physical therapist sets two different velocities of the treadmill belts for the sound and affected legs. In an experiment, eleven patients with chronic stroke participated in a short-term intervention trial (twenty gait cycles) of the developed treadmill system. Three of the five subjects who had lost balance between the stance phase of the sound leg and that of the affected one improved their gait balance in the intervention trial. In addition, one subject kept the well-balanced gait after the intervention. In the future, the algorithm to automatically adjust the belt velocities of the affected and sound sides and better biofeedback system with the sound leg information will be developed.