The reliability and validity of a Japanese version of the Matthews Youth Test for Health (MYTH) are reported. The MYTH is a questionnaire by which the degrees of Type A in children are measured. In Study 1, 23 teachers in kindergartens and day nurseries rated their children (N = 482 in all; 3 to 5 years old) by using the MYTH. Statistical analyses of the data indicate that this questionnaire is reliable and internally consistent, and has two factors, competitiveness and impatience-aggression, just as the American version. In Study 2, children (4 to 5 years old) were divided into two groups, Type-A (N = 24) and Type-B (N = 25), according to the scores of the MYTH. Each child was given three tasks (mailing, discrimination, and putting-in-chips). The results show that in those tasks Type-A children show more time urgency, hard-driving, and competition than Type-B children, which suggests that the Japanese version has a high construct validity. These two studies indicate that the Japanese version can be used in Japan to study Type A of young children.