While pre-service teachers’ beliefs about different dimensions of English language teaching have been widely researched, little is known about their beliefs related to English for Specific Purposes (ESP). This article reports on three Vietnamese pre-service teachers’ beliefs about ESP teaching, captured over a six-month period. Data from semi-structured interviews, stimulated recall interviews, observations, and reflective journals were collected at two critical points in the teacher education programme: the methodology course and the practicum. The findings add fresh insights into pre-service teachers’ beliefs, particularly how these beliefs may change over time. The three case studies presented in this paper illustrate how participants developed their beliefs. The six belief changes identified are then discussed in terms of levels (from no to significant change) and the underlying motives. Implications are also discussed for teacher educators in designing or improving teacher education programmes and for researchers interested in pre-service teachers’ belief change.