Nutrition studies were made on four divers performing a helium-oxygen saturation dive to a simulated depth of 200m in a hyperbaric chamber for about seven days. Daily intake of food was surveyed by regular weighing method and its calories and nutrients were calculated from Chinese food composition table. Fasting blood and 24h urine samples were collected on several occasions before, during and after the dive for estimation of free amino acid, nitrogen and minerals. Vitamin load test was conducted for evaluation of vitamin status. The results showed that during the dive intakes of cereal, meat and oil of divers were decreased, but vegetable, fruit and beverage intakes increased. An average body weight loss of 1.75 kg was found after a 7-day period, but little changes in the body fat. Free amino acid levels of serum and urinary output were reduced, especially the essential amino acids. The urinary excretion of minerals was in an acceptable range, but thiamin decreased markedly and not returned to an acceptable range until 10 days after leaving the hyperbaric chamber.