This study explores the relationships among teachers' beliefs about teaching science, learning science and the nature of science. Through interviewing 37 Taiwanese science teachers, teachers' beliefs about teaching, learning and science were respectively categorized as either 'traditional', or 'process', or 'constructivist'. It was found that most science teachers had 'traditional' beliefs. Moreover, more than a half of the teachers held views about teaching, learning and science that were closely aligned. This study, hence, called these closely aligned beliefs as 'nested epistemologies'. This study also suggested that the 'nested epistemologies' tended to be found in teachers of greater teaching experiences. It is suggested that the 'nested epistemologies' affect teachers' perceptions of the practice of science instruction.