This paper focuses on examining prospective science teachers' content knowledge about image formation in plane mirrors in terms of approach to error. In accordance with this purpose, 15 questions about the conceptual understanding of the image in plane mirrors and a data collection tool containing correct or incorrect information in the answers for each question were prepared and applied to the teacher candidates. The phenomenology, which is a qualitative research design, was used in this study. The sample consisted of 36 prospective teachers who continued their education in 3rd and 1st grades at a university in Turkey. The findings obtained in the research were analyzed with the descriptive analysis method. In the study, it was seen that the percentage of the candidates who were able to identify the questions that presented correct or incorrect answers about the image in plane mirrors was at a moderate level. Among the participants who detected incorrect answers in the questions presented to the candidates, it was determined that the explanations written by a small number of participants regarding the solution to the questions were correct. Most of the participants have misconceptions such as "the image is formed on the mirror surface in a plane mirror", "the image of objects in mirrors only occurs when the observer looks towards the mirror and does not occur when he does not", and "the size and location of an object's image in plane mirrors are affected by the movement of the observer". In the study, it was determined that some participants had the misconception of "seeing the mirror as a light source", which was not encountered in the literature. From the findings, it was stated that the participants in the research group were not in an acceptable position in terms of the image in plane mirrors, including their development in subject knowledge and student understanding. At the end of the study, some suggestions were made to researchers interested in the subject.