This paper traces 120 student teachers' professional identity transformation during practicums in China and US. By eliciting the participants' 240 written metaphors at the start and the end of the teaching practicums respectively, this study reveals the change of the embodied metaphors revolving around four arenas: (1) from idealistic expectations of teachers' roles to authentic perceptions; (2) from the felt inadequacy of professional knowledge and capability in teaching to varying professional growth; (3) from the transition shock to professional identity adjustment; and (4) the dynamic relationship with the school-based mentors. Meanwhile, this project found that the Chinese and American student teachers' professional identity transformation is a continuous process of interpretation and re-interpretation of professional experiences, which involves the interaction between person and socio-political context. The process is also idiosyncratic and is replete with identity construction. Implications for facilitating student teachers' professional identity transformation are discussed.