A one-legged training model was adopted to assess the influence of moderate-intensity exercise training on subcutaneous adipose tissue, especially focusing on the trained limb. Eight young sedentary Japanese women (ages 21–23 yr) participated in a 12-week training program. The leg was assigned randomly to trained or untrained limb. Each subject performed a supervised 60-min one-legged cycle ergometer training session three times a week. The exercise intensity was set at approximately 40% of peak VO₂ (“moderate” intensity, i.e., below the estimated lactate threshold), which was determined before training. Each subject performed a one-legged incremental cycle exercise test until exhaustion to determine the peak VO₂ of each leg (the trained and untrained legs being investigated separately). The areas of subcutaneous fat and the remaining nonfat tissues of the thigh were evaluated by our novel visualized measuring system based on ultrasonography. The fat cross-sectional areas of the trained and untrained thigh were not different after training (trained: 68.6±17.8 vs. untrained: 68.3±18.5 cm²). The non-fat (muscle and bone) area was also similar between the trained and untrained limb. In addition, there was no systematic influence of the training on the total and lean body mass. After training, the duration time of the one-legged cycle incremental exercise test by the trained leg was significantly improved unilaterally (trained: 1049±122 vs. untrained: 930±109 s, p <0.05) without any difference of peak VO₂. The results indicate that moderate one-legged aerobic training did not induce any compositional change in the trained thigh; rather, what did improve were certain peripheral factor alone relating to endurance.