Models and modelling play a critical role in science education to engage students more fully in science practices. Few studies have investigated the nature of models and modelling in integrated STEM teacher education. This study examines pre-service science teachers' (PSTs) understanding of the nature of models and modelling in a STEM methods course. Model and modelling for authentic STEM are used as a theoretical lens for conceptualising PSTs' understanding of the nature of models and modelling. Interpretive research was used to analyse how this course contributed to PSTs' understanding of the nature of models and modelling based on four dimensions: meanings, purposes, processes and the complexity of models and modelling. Data were collected through questionnaires. Inductive content analysis was used to reveal distinct patterns of PSTs' understandings. The findings indicated that at the beginning of the course, PSTs understood that models were a replication of phenomena or a prototype. By the end of the course, they understood modelling as a practice to explain and predict phenomena in science to solve problems and improve the quality of life through engineering. By the end of the course, PSTs viewed modelling as a bridge between science and engineering within the context of an integrated STEM education. The PSTs showed marked shifts by the end of the course by demonstrating a deeper understanding of modelling as a dynamic process. PSTs saw the integration of science and engineering in STEM as a route for epistemic agency on behalf of their students and a greater appreciation of model complexity. This study suggests that introducing the nature of modelling in science and engineering assists the teaching of STEM. The model and modelling implications for STEM teacher education are discussed.