The subcutaneous fat thickness was investigated to obtain the general characteristics of Japanese fat distribution by sex and age. Our subjects consist of 1, 477 males and 1, 933 females of all age groups in various localities in Japan. The newly developed A-mode type ultrasonic instrument was utilized to measure fat thickness including such locations as biceps, triceps, subscapula, suprailiac, thigh anterior, thigh posterior, and calf. The data obtained were analyzed by mean, standard deviation, and percentile. Our findings are summarized as follows: 1) It is confirmed that the subcutaneous fat layer of females is thicker than that of males. 2) Examining the ratio of upper-arm and trunk in subcutaneous fat layer, i.e. (biceps+triceps)/(subscapula + suprailiac), the adults' ratios are smaller than those of infants, and adult males accumulate more fat abdominally than adult females do. 3) The percentiles we obtained will provide the criteria for subcutaneous fat thickness of the Japanese by sex and age.