The University of Yonsei College of Medicine is implementing a new undergraduate curriculum that emphasizes active, self-directed learning. The aims of this study were to investigate the factors affecting problem-based le arning(PBL). We surveyed 169 senior students of medical college in Yonsei University. Among them, 137(82.0%) students answered. We developed a question form on seven areas, centering the factors affecting problem-based learning: small-grouping learning, teachers, teaching-learning environments, learning methods, working problem, assessment, the awareness on the problem-based learning method. Those questions were developed as five point scale and were conducted on April 26, 1997. The results of this study are like this: First, the factors affecting problem-based learning appear as working problem, teaching-learning environments, teaching-learning materials. Second, no difference based on working problem form was found. However, the group which used Harvard Working Problem proved to be think more positively than the group which used Illinois Working Problem. As the most important factors affecting problem-based learning appeared as working problem, teaching-learning environments and learning materials, so we should develop the environments and materials promoting self-regulated learning. Finally, the continuous and systematic study on problem-based learning is needed.