Teachers' pedagogical practice and choices for their actions could not only be explained by their knowledge, beliefs or attitudes (Rodgers & Scott, 2008). Identity also has a crucial role in learning to teach. The aim of this study is to investigate contextual nature of preservice mathematics teachers' professional identities. For this aim, a case study was designed. Participants are three preservice mathematics teachers in a state university in Turkey. The data was collected through semi-structured interviews. Pre-interviews were conducted in the beginning of the data collection process. Participants were asked questions about why they chose teaching as a profession. During the following ten weeks, preservice teachers participated in activities such as teaching in real classroom settings, interviewing pupils, mathematics teachers and school administrators. Following these activities, post-interviews were conducted. Qualitative content analysis was used to analyze the data. The findings revealed that preservice teachers' identities were not stable throughout different contexts.