This study aimed at investigating the role of self determination of the vocational school’s principals in improving the graduates’ competences, as well as factors that might influence such self determination. The self determination of a vocational school’s principal is a core component for a study because a principal with strong self determination will tend to work hard in order to achieve the visions and missions of the vocational school. The data were analyzed using descriptive statistics over 110 respondents who were sampled randomly from the total of 154 principals of vocational schools in Medan. The findings of the study indicate that the self determination of the vocational school’s principals is categorized as good. Meanwhile, factors which might contribute to the construction of such self determination are as follows: 1) they are determined to work hard until they achieve the goals, 2) they are highly initiative in solving problems, 3) they are humble, 4) they can control and manage all things for completing their duty, and 5) they can cope with stress. The attempt that the principals made in improving their graduates’ competences is by providing follow-ups to the results of supervisions in order to improve the learning. Also, improving their diligence in solving problems by initiating new ideas, and improving the determination to work hard by developing the willing to solve problems which might occur in school and by not putting off any responsibilities, as well as by appreciating other people’s contribution are the kinds of success they have achieved in improving their attempts to improve their graduates’ competences.