Purpose: To investigate the effects of repeated-sprint training in hypoxia vs in normoxia on world-level male rugby union players’ repeated-sprint ability (RSA) during an international competition period. Methods: A total of 19 players belonging to an international rugby union senior male national team performed 4 sessions of cycling repeated sprints (consisting of 3 × eight 10-s sprints with 20 s passive recovery) either in normobaric hypoxia (RSH, 3000 m; n = 10) or in normoxia (RSN, 300 m; n = 9) over a 2-wk period. Before and after the training intervention, RSA was evaluated using a cycling repeated-sprint test (6 × 10-s maximal sprint and 20-s passive recovery) performed in normoxia. Results: Significant interaction effects (all P < .05,