Abstract: AIM:To observe the effects of hyperbaric oxygen therapy on the heart rate variability in military personnel on the plateau. METHODS: Thirty-one military personnel coming down from the plateau to Lintong Sanatorium were divided into two groups: hyperbaric oxygen therapy group with normal recuperative+hyperbaric oxygen therapy and the normal recuperative group. Heart rate variability was detected at days 1, 15 and 30 and statistical analysis was conducted. RESULTS: No significant difference was observed in the heart rate variability in the normal recuperative group. Although a significant difference was observed in low frequency component (LF), low frequency component in normalized unit (LFn) and high frequency component in normalized unit (HFn) at the 15th day compared with those at the 1st day (P<0.05), no significant difference was found by the 30th day. No significant difference was found in heart rate, high frequency component (HF), LF/HF and total power spectral area (TP), LF, LFn and HFn at the 15th day compared with those at the 1st day (P<0.05), no significant difference was found by the 30th day. No significant difference was found in heart rate, HF, LF/HF and TP during the 30 days in the hyperbaric oxygen therapy group. HFn decreased significantly at the 15th day compared with that at the 1st day (P<0.05) and then rose. But no significant changes were seen between the 15th and the 30th day. CONCLUSION: Fifteen-day hyperbaric oxygen therapy can markedly improve heart rate variability in military personnel recently coming down from the plateau.