: Self-Development Aid to Improve Teachers' Competences and Students' Personality Development. This study was designed to develop a self-development aid to enhance teachers' competence and to develop personality tendencies of senior high school students. A preliminary study was carried out to measure teachers' competence in implementing guidance-and-counseling services to students and students' personality tendencies. The next step was to design self-development aid and to examine the effectiveness of the product. This study has yielded a product consisting of teacher guidance, student guidance, and assessment guidance which were found to be effective in improving teachers' competence in performing guidance and counseling services and in developing the personality tendencies of senior high school students. The products can be used directly by teachers in implementing guidance and counseling services in order to develop the personality of high school students.