We compared physiological and perceptual responses, and stride characteristics while walking backward in water with those of walking forward in water. Eight males walked on an underwater treadmill, immersed to their xiphoid process level. Oxygen uptake ((.)V(O2)), respiratory exchange ratio (R), heart rate (HR), minute ventilation ((.)V(E)), blood lactate concentration (BLa), ratings of perceived exertion (RPE: for breathing and legs, RPE-Br and RPE-Legs, respectively), blood pressure (for systolic and diastolic pressures, SBP and DBP, respectively), and step frequency (SF) were measured. In addition, step length (SL) was calculated. (.)V(O2), R, HR, V (E), BLa, RPE-Br, RPE-Legs, and SBP were significantly higher while walking backward in water than when walking forward in water (P<0.05). Furthermore, SF was significantly higher (P<0.001) and SL was significantly lower (P<0.001) while walking backward in water, compared to walking forward in water. These results indicate that walking backward in water elicits higher physiological and perceptual responses than those produced when walking forward in water at the same speed.