Pedagogical Content Knowledge (PCK) as combines a teacher's knowledge of teaching and content so that the specific content is easy for students to understand. This study aimed to investigate the teacher's PCK in teaching decimals after mentoring by the research center of the Indonesian Realistic Mathematics Education (PRP-PMRI) team. This qualitative study involved two teachers teaching fourth grade at the school partner of PRP-PMRI, Aceh Province, Indonesia. The participation was voluntary, and the teachers had attended training related to the implementation of RME. Data were collected by observing during learning, interviews, reflection, tests, and interviews. This study showed that teachers' PCK in teaching focused more on the reality principle, activity principle, interactivity principle, and guidance principle of RME. They paid less attention to the other RME principles: level principle and intertwinement principle. The teacher also lacked experience making students' conjectures and did not prepare strategies to anticipate them. The teacher also paid less attention to identifying students' ways of thinking. In addition, the teacher's knowledge about the content was also unsatisfactory. This study also revealed that teachers' content knowledge also influenced teaching strategies, leading to students' misconceptions. This research implies that mentoring to improve teachers' PCK needs to be carried out continuously.