The advantages of nasal high-flow oxygen therapy (NHF) include not only allowing talking, but also eating and drinking, during the therapy. However, the effect of NHF on the swallowing reflex remains unclear. In the present study, we aimed to assess the effects of NHF on the swallowing reflex. Nine healthy adult Japanese male volunteers with no history of dysphagia or diseases that may cause dysphagia, such as stroke or Parkinson's disease, were evaluated. Participants received one of four levels of NHF intervention (0 (control), 15, 30 and 45 L/min of oxygen) with the NHF system through the nasal cannula. Swallowing was induced by the administration of a bolus injection of 5 mL of distilled water over 3 s through a polyethylene catheter at each level of oxygen flow. The primary end-point was the latency period of the swallowing reflex after bolus injection, which was defined as the time from the start of the bolus injection to the onset of the electromyogram (EMG) burst of the first swallow. Mean latency times of the swallowing reflex with 15 (9.8 +/- 2.9 s), 30 (9.0 +/- 2.7 s) and 45 (8.5 +/- 3.0 s) L/min of NHF were significantly shorter than those under control conditions (11.9 +/- 3.7 s; P < 0.05). Our study demonstrates that NHF may enhance swallowing function with increasing levels of NHF by reducing the latency of the reflex. NHF may allow continuation of oral intake without aspiration during oxygen therapy.