An adequate understanding of the nature of science (NOS) has become increasingly important for science teachers in South Africa as comprehensive curricular reforms over the past decade include promoting informed understandings of the ontological and epistemological bases of scientific knowledge and the methods of science. The main objective of this study was to explore the NOS understandings held by a sample of science teachers in the Eastern Cape Province of South Africa. Data were generated via questionnaires (n=136), semi-structured interviews (n=31), and classroom observations (n=8). The teacher interviews, which were informed by the questionnaire data, enabled further interrogation of the teachers’ philosophical positions. Their classroom practices were examined within the framework of these philosophical positions and the requirements of the new curriculum. The effect of implicit and explicit instruction in NOS on these teachers’ beliefs and classroom activities was also considered. A mixed-method approach informed by positivist and interpretivist perspectives was used for the collection and analysis of the data. The data suggests that explicit instruction in NOS resulted in more informed conceptions of science and the scientific enterprise, and that these conceptions were reflected, to a degree, in their classroom behaviours. However, it was noted that the teachers in this study often held philosophically eclectic views of the nature of scientific knowledge and how scientists develop ideas. Similarly, the South African National Curriculum Statement portrays science in contrasting ways, i.e. often within a modern/realist framework, but in other instances within postmodern/relativistic understandings (particularly in terms of indigenous knowledge systems). As such, an approach which aims at providing a firm foundation for understanding NOS ideas within a modern/realist perspective before emphasising the postmodern/relativist aspects of the scientific enterprise is suggested for teacher training and curriculum development.