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We analyzed the effects of 4-week H2 inhalation on cognitive performance in women aged 65 and above. The participants (n = 13) were community-dwelling older women (age 68.0 ± 3.0 years; weight 66.9 ± 10.3 kg; height 161.1 ± 5.8 cm) who volunteered to participate in this open-label pilot trial (, NCT02830854). The participants received H2 by inhalation for 15 min once per day for 4 weeks. The cognitive function was assessed using the Mini Mental State Exam (MMSE) and Alzheimer disease assessment scale cognitive subscale (ADAS-Cog) at baseline and at follow up. H2 intervention significantly increased total MMSE scores (for 14.2% on average; p < 0.01), thereby improving cognitive function from mild dementia at baseline (a score of 25.6 out of 30) to normal cognition at follow up (above a cut score of 27). In addition, ADAS-Cog scores were significantly improved by H2 inhalation, with better performance for word recall test (p < 0.01), and improved word recognition (p = 0.01) at post-administration, respectively. This pilot trial seems to corroborate previous animal studies, suggesting that gaseous H2 might be considered as a beneficial agent for age-related cognitive health.