This qualitative study seeks to explore how two university English-as-a-foreign-language (EFL) teachers learned to teach critical thinking (CT) through lesson study in China. Informed by relevant literature on CT and teachers' learning to teach CT, and drawing on data from interviews, classroom observation, artefacts and research journals for one year, this study revealed that the two teachers began their learning journeys in different ways, but gradually shared similar trajectories after they joined lesson study projects, and that lesson study was facilitative for the teachers to improve CT instruction pedagogy. The study concludes with implications for supporting in-service EFL teachers' learning to teach CT through lesson study.