ABSTRACT Background and objective We hypothesized that by reducing respiratory work and improving gas exchange, nasal high flow (NHF) would improve exercise tolerance in patients with chronic obstructive pulmonary disease (COPD) following respiratory exacerbation. Methods This was a monocentric, randomized, controlled crossover study. Patients with severe to very severe COPD carried out two high‐intensity constant work‐rate exercise tests (CWRET) with and without NHF on two consecutive days. The primary outcome was the mean difference in endurance time between both conditions. The secondary aims included vastus lateralis oxygenation (StO 2 ), dyspnoea, leg discomfort, maximal inspiratory pressure (MIP), transcutaneous CO 2 pressure (PtcCO 2 ), respiratory rate (RR), heart rate (HR) and pulsed O 2 saturation (SpO 2 ), as well as the patients' opinions of the device. Results A total of 19 patients were included (mean forced expiratory volume in 1 s = 28.7 ± 10.8%, age = 62.1 ± 9.1 years). No significant differences in endurance time during the CWRET were found between the two test conditions (−66.58 (95% CI: −155.9 to 22.7) s, P = 0.12). StO 2 , PtCO 2 and HR were reduced at the end of the exercise with NHF (−2.1% (95% CI: −4.3 to −0.0); −1.3 mm Hg (95% CI: −2.5 to −0.2); −2.7 bpm (95% CI: −5.0 to −0.5), respectively, P ≤ 0.05). No significant differences were found for any of the other secondary outcomes. Half of the patients evaluated the device as being moderately to very uncomfortable. Conclusion NHF during exercise did not increase endurance time in patients with COPD following exacerbation. Clinical trial registration NCT03058081 at clinicaltrials.gov