This study is to explore the PCK (Pedagogical Content Knowledge) of novice high school science teachers and to analyze how PCK is actually expressed in the classroom by comparing and analyzing the teachers’ PCK and science class practices. The subjects of this study were two novice high school science teachers. The data were collected through classroom observation, CoRe (Content Representation)-based questionnaire, teachers’ questionnaire, and semi-structured interviews. The collected data were analyzed on the components of PCK, including the orientation toward teaching science, knowledge and beliefs about science curriculum, teaching strategies, learners, and evaluation. The results of the study indicated that the PCK of the, one of the two subjects’ (Teacher Bae) orientation toward teaching science was expressed differently in the actual classroom. Other PCK components, such as knowledge and belief of teaching strategy, learner, and evaluation were not expressed fully in the classroom environment. In the case of the other subject (Teacher Yoo), the direction of science teaching was consistent with the actual practice of in the classroom. Also, the knowledge and beliefs about teaching strategy, learner, and evaluation were influenced by an orientation toward teaching science, which was reflected in class practice. The teacher s PCK seemed to be influenced by the teacher s personal orientation and teaching experience. Moreover, less constrained and free atmosphere of the school played a significant role. Therefore, by encouraging teacher training, teachers’ autonomy in classrooms, and comfortable school atmosphere, PCK of the novice high school science teacher can be formed in accordance with the characteristic of the subject and fully manifested in the actual class practice.