Purpose: Critical thinking (CT) is defined as the use of higher cognitive skills to determine appropriate action. We designed a novel forum curriculum to cultivate CT for medical students through academic debate. Methods: The developed forum curriculum included a background knowledge test, student group debate, expert debate demonstration, and discussion. Learning attitude, learning motivation, collective efficacy, and CT questionnaires were measured pre- and post-forum. The overall satisfaction of the forum curriculum was also measured post-forum. We analyzed the differences in the pre- and post-forum and group debate scores using paired t tests. The predictors of the outcome were analyzed by regression. Results: The mean scores of learning attitude, learning motivation, collective efficacy, and CT, measured after the forum curriculum, were significantly higher than those measured before the curriculum (p < 0.001). In the regression model, we found that participants who had experience of team-based learning (TBL) classes had higher CT scores than those who had no experience of TBL. Moreover, the mean of previous academic grades was a significant predictor of group debate performance score. The overall satisfaction of the forum curriculum was 8.8 points out of 10 points. Conclusions: Our study demonstrated that academic debate as part of a forum curriculum may help medical students develop CT skills, which will equip them to deal with clinical uncertainty. Further large-scale, randomized studies are necessary to confirm the beneficial effects of the forum curriculum.