While there has been an increasing number of graduate students who enter teacher education after obtaining a higher research degree (e.g., PhD or EdD), scant attention has been paid to their professional learning as prospective teacher educators in higher education. To fill this gap, this study, informed by the social theory of learning, investigates how three PhD students learned to become teacher educators in a university in China. Drawing on the data from interviews and the participants' personal reflections, the study shows that the participants engaged in professional learning by interacting with different others (e.g., teachers and teacher educators), negotiating and tuning their enterprise, and developing a repertoire of knowledge and skills in their communities of practice. The study generates some implications for both teacher education and higher education in preparing and developing future teacher educators.