Background <p>Pulmonary imaging plays a critical role in clinical diagnosis, and developing diagnostic reasoning skills is a key objective of undergraduate medical imaging education. Traditional lecture-based learning (LBL) may be insufficient to actively engage students or to cultivate higher-order diagnostic abilities. This study aimed to evaluate the effectiveness of a case-based learning combined with flipped classroom (CBL-FC) approach in teaching pulmonary imaging diagnosis to undergraduate medical students.</p> Methods <p>A prospective, quasi-randomized controlled study was conducted involving 26 third-year undergraduate students majoring in Medical Imaging. Due to the method of allocation based on the parity of student ID numbers, students were assigned to either a CBL-FC group (<i>n</i> = 13) or an LBL group (<i>n</i> = 13). The teaching content focused on imaging diagnosis of common pulmonary diseases. Learning outcomes were assessed using pre- and post-intervention tests evaluating theoretical knowledge, application of imaging principles, and diagnostic reasoning based on clinical cases. Students’ learning experiences and satisfaction were assessed using a self-administered questionnaire based on a 5-point Likert scale.</p> Results <p>There was no significant difference in baseline test scores between the two groups (<i>p</i> = 0.150). After the intervention, both groups demonstrated improved performance; however, post-intervention test scores were significantly higher in the CBL-FC group compared with the LBL group (<i>p</i>&lt;0.001). No significant difference was observed between the two groups in theoretical knowledge (<i>p</i> = 0.628). In contrast, students in the CBL-FC group showed significantly better performance in the application of imaging principles and diagnostic reasoning based on clinical cases. However, the small sample size may limit the statistical power and generalizability of these findings. Future studies with larger sample sizes would help to confirm these results and assess their broader applicability. In addition, students in the CBL-FC group reported high levels of learning interest, positive learning experiences, and overall satisfaction with the teaching approach.</p> Conclusions <p>The CBL-FC approach appears to be a feasible and potentially effective teaching strategy for undergraduate pulmonary imaging education. By promoting active participation, peer interaction, and diagnostic reasoning, this approach may support the development of clinically relevant imaging interpretation skills.</p>