This study compared the body water turnover in endurance athletes and age-matched sedentary men. Eight competitive endurance athletes (20.8±1.9 yr) and age-matched eight sedentary men (21.6±2.5 yr) participated in this study. Total body water and body water turnover were measured using the deuterium (D₂O) dilution technique. Urine samples were obtained every day for 10 days after oral administration of D₂O. The day-by-day concentrations were used to calculate the biological half-life of D₂O and body water turnover. Maximal oxygen uptake (VO_2max) and oxygen uptake corresponding to ventilatory threshold (VO_2VT) as an index of aerobic capacity were determined during a graded exercise test. Both VO_2max and VO_2VT were higher in the exercise group than in the sedentary group ( P <0.05). The biological half-life of D₂O was significantly shorter in the exercise group than in the sedentary group (5.89±0.81 days vs. 7.52±0.77 days, P <0.05), and the percentage of the body water turnover was significantly higher in the exercise group than in the sedentary group (11.99±1.96% vs. 9.39±1.21%, P <0.05). The body water turnover was correlated with VO_2max and VO_2VT, respectively ( P <0.05). Based on these findings, this study speculates that a level of physical activity may induce a body water turnover higher in the healthy state, since the better trained subjects have a higher body water turnover.