The differences between the effects of high- and low-intensity exercise training on cardiorespiratory system and serum lipid levels were examined under conditions in which the total work load was same. Twenty-two healthy, untrained female students, aged 18 to 24 years, participated in the 8-week training experiment. Two training groups exercised on bicycle ergometers 4-5d/wk for 8 wk with high-intensity (H: 70% VO2 max 13 min/session; N = 8) or in low-intensity (L: 36% VO2 max 33 min/session; N = 8). The control group (C: N = 6) continued its sedentary life style. Data of 6 students (H: N = 2, L: N = 2, C: N = 2) were excluded from the analysis, because they did not carry out their duties. The results of this study were as follows; 1) Aerobic capacity increased in both training groups. 2) After training, both heart rates and oxygen uptake during submaximal work loads significantly decreased in group H, but only heart rates significantly decreased in group L. 3) Heart rates with a same oxygen-uptake load during submaximal work seemed to increase in group H, but significantly decreased in group L. 4) The mechanical efficiency during the submaximal work load significantly increased in group H, but not in group L. 5) DBP and MBP during the submaximal work load in group L significantly decreased compared with those before the training. SBP with a same oxygen-uptake load during submaximal work increased in group H, but decreased in group L. 6) Rate pressure products both at rest and during submaximal exercise decreased significantly in group L. 7) Serum lipid levels remained in all groups. These results suggested that when the amount of exercise is the same, low-intensity exercise training with 35% VO2 max was more effective to increase endurance capacity and was safer than high-intensity exercise training.