A set of 14 body dimensions and 9 their indexes were obtained and compared between the groups of Thai 80 males and 115 females (aged 16 to 18 years), and Japanese 50 males and 55 females (aged 15 to 18 years). The body weight, height, acromial breadth, chest girth, arm girth, thigh girth and calf girth for Thai males or females are significantly smaller than those of Japanese males or females respectively. The body indexes such as (upper limb length) / (height), (trochanteric height) / (height) and (forearm girth) / (arm girth) for the Thai males or famales are significantly larger than those of Japanese males or females. The principal component analysis revealed that the total body size (the first principal component) was the largest for Japanese males and decreased in the following order of Japanese females, Thai males and Thai females. These physical differences indicate that a careful application of the sizing systems for clothes in Japanese Industrial Standard or International Standard Organization to young males and females in Thailand are needed.