Teacher identity is an emerging subject of research interest in the field of teacher education and teacher development. Teacher identity, as an ongoing, shifting and dynamic process, is complex and multi-faceted. As a result, teachers' perceptions of their identity vary from different perspectives and endure a changing process with the accumulation of their teaching experiences. The changing process is in fact the process of the construction of how they perceive themselves - their identities. This study employs three EFL teachers with different lengths of teaching experiences as cases. Through observations of their teaching life and interviews, this study aims to explore: 1) How do teachers perceive their identity? 2) How do these perceptions change and whether this changing process influences teachers' behavior? 3) What are the possible stages or phases of the process? 4) What are the possible factors that influence the construction process?