Science teachers need an adequate understanding of nature of science (NOS) and the ability to embed NOS in their teaching. This collective case study aims to explore in-service science teachers' conceptions of NOS and the embeddedness of NOS in their teaching about astronomy and space. Three science teachers participated in this study. All participants attended the NOS workshop based on an explicit-reflective approach. They were asked to respond to the Myths of Science Questionnaire on three different occasions, i.e., at the beginning and the end of the NOS workshop and a semester after the workshop. Classroom observation, interviews after teaching, and a collection of related documents were also employed to collect data. The data were analyzed using a constant comparative method. The results revealed two important assertions. First, science teachers' conceptions of NOS are stable and resistant to change. However, an explicit-reflective approach employed in the NOS workshop, to some extent, promoted science teachers' understanding and reasoning about NOS. Second, science teachers' conceptions of NOS are not directly related to their classroom practices. With different degrees of NOS understanding, all participants taught NOS implicitly and missed most of the opportunities to address aspects of NOS embedded in the topics they taught. The implications of these findings are also discussed.