No study investigates whether low-volume HIE including repeated-sprint exercise (RSE) in hypoxia has an extra effect on body composition and metabolic risk factors when compared with normoxia. METHODS A double-blind randomized controlled experimental design was used to conduct a 5-week RSE intervention in normobaric hypoxia simulated an altitude of 2500m or sham normoxia at sea level. 24 obese young women completed all 20 sessions either in hypoxic (RSH, N=11) or normoxic repeated-sprint exercise training (RSN, N=13), which comprised 8 s of sprinting and 12 s of rest with a maximum of 60 repetitions in 20 min for four days each week. Body composition measured by DEXA and blood samples were assessed at pre- and post-intervention in the follicular or luteal phase of menstrual cycle. Physical activity and food diary were estimated during the study. RESULTS There were no within- and between-group differences in daily energy intake and physical activity at pre-, during-, and post-intervention times (p > 0.05). Five weeks of RSE resulted in significantly improvements in absolute and relative V̇O2peak and maximal O2 pulse in both groups (p<0.01). The increments of V̇O2peak and maximal O2 pulse in RSH (∼20%) were twice as much as in RSN (∼10%) (p<0.05, d = 0.88-0.95). There were