The effects of glycine on sleep quality were examined in a randomized double‐blinded cross‐over trial. The volunteers, with complaints about the quality of their sleep, ingested either glycine (3 g) or placebo before bedtime, and their subjective feeling in the following morning was evaluated with the St. Mary's Hospital Sleep Questionnaire and Space‐Aeromedicine Fatigue Checklist. The glycine ingestion significantly improved the following elements: “fatigue”, “liveliness and peppiness”, and “clear‐headedness”. These results suggest that glycine produced a good subjective feeling after awakening from sleep.