The aim of the study is to examine how lesson study activities affect primary school preservice teachers' noticing of students' misconceptions. A qualitative research approach was adopted and action research method was used. The study was conducted with 9 primary school preservice teachers. The data were obtained from the observation form, video recordings, reflection reports and field notes in order to reveal how the lesson study model affected the noticing development of preservice teachers. In addition to these, the "video exam" at the end of the Teaching Practicum-II course also constituted one of the data collection tools. Descriptive analysis was used in the study. The data obtained were analyzed by adapting the theoretical framework of "Levels of Noticing of Students' Mathematical Thinking" developed by van Es (2011) as "Levels of Noticing of Students' Misconceptions" in order to reveal preservice teachers' noticing of students' mathematical thinking. As a result of the research, it was concluded that noticing skills of the lesson study group preservice teachers were mostly at the level of reasoning and justifying their reasons (level 3) and offering alternative pedagogical solution suggestions based on comments (level 4). It was concluded that the noticing skills of the comparison group preservice teachers were mostly descriptive (level 1) and at the level of identifying important events but being insufficient to expand their interpretations (level 2).