The aim of this study is to develop a pneumatic gait training system. This study report the prototype of pneumatic gait training system based on a modified long-leg orthosis and a treadmill system. The special pneumatic actuator, the similar actuator to human muscular system, was used as the actuator for hip and knee flexion/extension movement. This prototype system of pneumatic gait training is able to utilize for both land and underwater environments. We evaluated this system by the experimental test on land and underwater conditions. It is indicated from the experiment test that 1) the hip and knee joint movement patterns of both on land and underwater gait were quite similar kinematics for normal gait pattern, 2) the activity of lower limb muscles decreased across the gait cycle on land gait, 3) the activity of hip extensor and knee flexor muscles decreased during stance phase in underwater gait These results of this study suggest that the pneumatic gait training system might be effective for gait training to several motor disorders.