The Self-Acceptance Inventory (SAI), consisting of self-understanding, self-appraisal, self-worth, and self-confidence, was administered to junior high school girls (n=89) once a year in 1980, 1981, and 1982 respectively, for the purpose of investigating longitudinal development of self-acceptance. The self-understanding of the subjects tends to increase with the development, while the self-appraisal definitely decreases. The subjects understand their own negative character and appearance, but not positive aspects. They gradually become dissatisfied with themselves. High level of self-worth, however, is maintained: they fundamentally consider themselves to be worth as human beings. From the analysis of coefficients between the aspects of the SAI and its factor analysis, the self-understanding and self-confidence are found to be stable aspects while self-acceptance is gradually differenciated.