The purpose of this study is to find out personality traits that are supposed to provide pupils' academic achievement. For that purpose, especially for the over-achievers, an investigation was carried on for thirteen traits of "Behavior Records" in "Guidance Digest" and fourteen traits of mental hygiene. The academic achievement was determined by the results of Japenese and arithmetic evaluated by the teachers, other personality traits were determined by pupils' own self-evaluation expressed in the questionnaire. The subjects for this investigation were 2330 school children of the fourth, fifth, and sixth grades who were divided into 570 over-achievers, 1195 normal-achievers, and 565 under-achievers. As for the personality trait that were evaluated by these three group achievers, the χ^2 Test was used to judge the difference between the groups, while the fundamental traits which were the features of over-achievers were abstracted by the factor analysis. Results : The results can be summarized as follows : No significant difference was found in both results of the χ^2 Test and factor analysis between over-vs. normal-achievers, normal-vs under-achievers, but that difference was noticeable between over-vs. under-achievers. These significant traits were integrated into three personality dimensions. They were : (1) a dimension of general self-concept : independence, self-respect, elevation, positiveness, self-control, endurance, and introversion thinking. (2) a demension of emotional adjustment : sense of self-importance, inferiority complex, excitability of feeling, depression, nervous prostration, security of emotion, and sentiment. (3) a demension of social adjustment : responsibility, cooperation, school adjustment, and family adjustment.