This study aims to investigate pre-service physics teachers' metacognitive knowledge about their teaching practices. The participants included six pre-service physics teachers. A taxonomy of metacognition for teaching was developed to analyze the level of pre-service physics teachers' metacognitive knowledge about their teaching practices. Analysis of data showed that pre-service physics teachers' metacognitive knowledge about their content knowledge was quite satisfactory; however, their metacognitive knowledge about instructional methods, students' pre-instructional knowledge, and the task of teaching needs to be improved. The results of the study provided evidence that metacognitive knowledge on teaching is a fruitful framework to generate interpretations about the participants' instructional processes.