With the purpose of assessing the development of dynamic nature of personality with individual differences, we have been gathering, by repeated tests and observations, the data from the same groups of subjects in the Attached Schools and Kindergarten of Kobe University Faculty of Education. This longitudinal study which began in 1968, will eventually cover a span of twelve years when one of our groups of subjects (aged 3 at the beginning of this study) have reached the age of fifteen (in the third and the last grade in the Attached Junior High Schaol). However, in the present reports the results of our analyses of the data obtained from the three-year period of personality development of the Junior High School Subjects were presented.In order to determine the relationship between sexual maturation and the subsequent changes in personality characteristics, we divided the whole sample of 121 junior high school subjects into five Type-groups, and for each of these groups, the longitudinal data obtained before and after the beginning of maturation (identified on the basis of changing of voice for boys and beginning of menstruation for girls) such as measures of physical growth, self-concept,general and vocational interests, interests in school subjects and personality traits were compared. The results revealed:1) As to the growth in stature, the same regular growth trend was found formost subjects, regardless of the differende in time of the beginning of puberescence. For an instance, maximum growth rate in standing hight was indicated in the growth-period just before the beginning of puberescence.2) Self-concept measured by Semantic Differential technique indicated a trend toward stabilization in 40% of the subjects while the reverse trend was found in other 30%. The remaining 30% indicated no marked change in their self-concept. However, there was no regular change in accordance with the arrival of puberescence.3) Measures of general and vocational interests indicated, as in the case of self-concept, irregular individual variations after puberescence. But, interests in school subjects tended to be stabilized in the course of the three years.4) Measures of personality traits obtained by means of two personality tests showed also a trend toward stabilization. But, no marked changes which were directly related to the arrival of puberescence could be found in our data.From these findings, it was concluded that such aspects of personality as interests, selfconcept and traits in personality do not change in a uniform and regular way just after the beginning of puberescence, as shown in the development of physical side of personality.