BACKGROUND: Peak oxygen uptake (VO 2peak) remains low after lung transplantation (LTx). We evaluated the effect of high-intensity interval training (HIIT) on VO 2peak , muscular strength, health-related quality of life (HRQOL), pulmonary function, and physical function after LTx. METHODS: In this randomized controlled trial, 54 participants were enrolled from 6 to 60 months after LTx. The HIIT group (n = 25) followed a supervised HIIT program, consisting of endurance and strength trainings 3 times a week for 20 weeks. The control group (n = 29) received usual care. The primary outcome was a change in VO 2peak measured by cardiopulmonary exercise testing. The secondary outcomes were changes in 1-repetition maximum (1RM) for arm press and leg press, HRQOL (36-Item Short-Form Health Survey [SF-36]), pulmonary function (forced expiratory volume in 1 sec, diffusing capacity of the lungs for carbon monoxide), and physical function (1RM in handgrip, 15-sec stair run, and 30-sec chair stand). RESULTS: A total of 46 participants completed the study, including 23 of 25 in the intervention group. For the primary outcome, the intention-to-treat analysis revealed a non-significant between-group difference for change in VO 2peak of 0.7 ml/(kg.min) (95% CI =-0.3, 1.8) (p = 0.17). The between-group differences for 1RM arm press and leg press and mental aspect of SF-36 were 4.9 kg (95% CI =-0.1, 9.9) (p = 0.05), 11.6 kg (95% CI = 0.1, 23.0) (p < 0.05), and 5.7 kg (95% CI = 0.9, 10.4) (p = 0.02), respectively. There were no between-group differences in pulmonary function or physical function. When excluding participants with an attendance of <70% (n = 16), the between-group difference for VO 2peak was 1.2 ml/(kg.min) (95% CI = 0.1, 2.4) (p = 0.032). CONCLUSIONS: HIIT improved muscular strength and HRQOL but did not improve VO 2peak more than usual care after LTx. However, with acceptable adherence, HIIT appears to have beneficial effects on VO 2peak .