There has been much discussion as to whether heredity or environment is the more influential factor in personality development of the individual: Clinicians as a general, insist on regarding the heredity as rather an influential factor. On the other hand, psychologists insist on regarding environment as rather an influential one. J. F. Brown (1936) once tried to unify these contradictory viewpoints by applying “Field Theory”. However, his attempt has seemed not to be accepted. And it was likely to be impossible, at that stage of experiment, to define the roles of these two factors for personality development.Consequently, a more comprehensive study of the relationship between heredity and environment seems to be needed, as is suggested by R. B. Cattell (1965).Under this circumstance, we, the members of Japan Women's University study group, have tried to investigate this problem by reviewing some of the experiments on animal psychology, in order to find how an experience of the infant affects his character formation. At the same time, we have proceeded to study a relation of child-rearing to character formation and the child-rearing as it is seen as determinant variable for the achievement drive of the individual child.