The aim of this study was to clarify the influence of buoyancy on physiological responses during treadmill walking. Six subjects participated in this experiment. The water level was adjusted to the greater trochanter. Normal water (NW) and 1.135 kg/l of specific gravity (high buoyancy ; HB) were set. Oxygen uptake (VO₂), heart rate (HR), and rating of perceived exertion were measured during exercise. VO₂ in HB at all walking speeds were higher than those in NW significantly. HR enhanced in HB over the walking speed of 70 m/min significantly. It was clear that the workload of walking in HB increased remarkably over the walking speed of 70 m/min. This suggested that the water resistance acted on the phenomenon of increase of the workload in HB. Furthermore, it was suggested that walking in HB was useful for rehabilitation and therapeutic exercise in the low-speed and for physical training in the high-speed.