Australian science teachers are asked to involve their students in the scientific processes of inquiry and investigation. The abilities needed for scientific problem-solving ("doing") and the capacity to reflect on the process of problem-solving at a meta level ("understanding") are defined as scientific reasoning competencies in this article. Science teachers need to have strong scientific reasoning competencies themselves to model and promote scientific reasoning competencies among students. Hence, scientific reasoning competencies have become an important element of science teachers' professional competencies. This article introduces the relevance of scientific reasoning competencies for science teacher education in Australia. In addition, it provides a theoretical approach of how to develop such competencies in pre-service science teacher education. Finally, an empirical case study on scientific reasoning competencies of pre-service science teachers at one university in Victoria is reported. The findings propose that the pre-service teachers have a reasonable level of scientific reasoning competencies themselves; however, there is no significant increase of this level during the first year of their Master of Teaching degree course. It is concluded that the development of scientific reasoning competencies is a long-term process, which might be supported by providing a sequence of appropriate problem-solving and accompanied opportunities of explicit reflections.