Patients with stroke exhibit a stiff-knee which characteristic is that knee flexion diminishes significantly during gait, particularly in the swing phase because loss of control ability. Ability of knee control is important during gait. In this paper we developed a Virtual Reality (VR) rehabilitation system for stroke patients who have a stiff-knee gait disorder. Developed VR rehabilitation system is able to measure knee joint angle and interact between system and patients using a marker-based measurement system composed of a PC and an IEEE1394 camera. To validate feasibility of VR system, we performed experiment using a treadmill with same speed (2.0 km/h) and various target angles (40 degrees, 50 degrees and 70 degrees). The purpose, we performed with various target angles, is that we ascertain that normal participants make a success of task with the abnormal target angle as well as the normal target angle. Four healthy male (age from 24 to 28 years) was recruited for this experiment. And experimental task was composed in three stages and we measured average of trial numbers for success in each stage. The trial numbers gradually decreased with each stage in 50 and 70 degrees. In conclusion we ascertained that VR system help with increasing control ability of knee joint of the participants at 50 and 70 degrees. From now on we expected that developed VR gait training is possible to use in practical gait training with stroke patients. Therefore we will need a clinical test to apply this system to stroke patients in hospital.