Contrary to most of European and American investigators failed to find out the seasonal variations of basal metabolic rate in man, Japanese and Korean investigators reported the increase in winter, decrease in summer season. But the causes of variation were not found clearly. To find out whether metabolic acclimatization to climate could be arise or not in human being, the basal metabolic rate was determined monthly for a period of one year in Airmen volunteers who live in Seoul, with 9 l Collins spirometer. The results obtained were as follows: 1. The average ambient temperature was lowest in February (-5.88℃) and highest in July (27.34℃). 2. Basal metabolic rate was lowest in June and highest in December showing seasonal variations. Interestingly, the increase of basal metabolic rate followed after the drop of ambient temperature below 0℃ (December) and the decrease followed after the elevation of ambient temperature from optimum to hot (June) or cold to warm (March). 3, Mean skinfold thickness increased in spring, decreased in winter. 4. These findings indicate that the basal metabolic rate of Korean reveals the seasonal variation affected by ambient temperature highly.