This article reports a classroom-based inquiry in which a group of pre-service language teachers were guided to engage in a lesson study project focusing on the incorporation of the framework of big ideas into language teaching. Specifically, the study zooms in on the student teachers’ exercise and development of critical thinking (CT) through the lesson study process. Relying on data from semi-structured interviews and classroom artifacts, the findings reveal that the introduction of big ideas in lesson study served as a crucial knowledge base for the participants’ pedagogical sense-making, thus contributing to their CT. The process of lesson study, characterized by a progressive structure, tailored scaffolding, and constructive feedback, also facilitated their development of CT skills and dispositions, which in turn contributed to their understanding and application of the big idea framework within the lesson study process. While the participants encountered some negative feelings in the process (e.g. due to the competitive atmosphere brought by the ‘same topic and different design’ arrangement), they tried to turn such emotions into a stimulating source for their CT growth and professional learning. In light of the research results, pedagogical implications for teaching and teacher education were put forward in the end.