To gain a better understanding of teachers' beliefs about teaching, as compared with their in-reality classroom practices, case studies were constructed with four science teachers in different schools in Egypt. The main aims of this article were to provide an answer to the research question, "To what extent do science teachers' beliefs correspond to their practices?" and to explore the contextual factors that can explain the difference, the consistency or inconsistency, between teachers' beliefs and practices. The study collected data for each teacher using semi-structured interviews, notes taken while observing classes, and teachers' notes, journals, and lesson plans concerned with STS lessons. The data were analysed using the constant comparative method around common themes, which were identified as distinctive features of teachers' beliefs; these same themes were then compared with their practices. Results showed that a few of the in-service science teachers' pedagogical beliefs aligned with constructivist philosophy. Some of the teachers' beliefs were consistent with their practices, especially the traditional beliefs, while some of teachers' practices were conflicted with their beliefs in different contexts. (Contains 1 table and 2 figures.)