If, like their counterparts in the primary and secondary sectors, vocational training teachers face significant challenges when entering the profession, their atypical career path, often paired with a lack of training in pedagogy, poses challenges for their professional life. This research was interested in vocational training teachers’ self-efficacy, a facet still unexplored, but relevant in the study of the development of their teaching competence. Through semi-structured interviews with 21 vocational teachers from Quebec, this research helped identify the most decisive sources of their self-efficacy. The results show that the mastery experiences, particularly the professional experiences related to the trade that they are teaching, seem to be what most influenced the participants’ beliefs of effectiveness.