Background:The importance of self-directed learning (SDL) and collaborative learning has been emphasized in medical education. This study examined if there were changes in the pattern of SDL and group cohesion from the time of admission to medical school under the criterion-referenced grading system, increased group activities, and interaction of medical education curriculum. Second, it was examined whether group cohesion influences selfdirected learning. Methods: The participants were 106 medical students (71 males, 35 females) who enrolled in Yonsei University College of Medicine in Seoul, South Korea in March 2014. They were asked to complete a Korean version of the self-directed learning readiness scale (SDLRS) and group cohesion scale (GCS) at the end of each semester for three years. A repeated measures ANOVA and a correlation and regression analysis were conducted. Results: All the participants completed the questionnaires. There were differences in the SDLRS scores over the three years. A significant increase was observed one year after admission followed by stable scores until the third year. There was a significant increase in GCS scores as students progressed through medical school years. Positive relationships were found between SDLRS and GCS scores, and the regression model predicted 32% variance. Conclusions: SDLRS and GCS increased as medical school years progressed. In addition, GCS is a significant factor in fostering SDLRS. Medical schools should develop various curriculum activities that enhance group cohesion among medical students, which would in turn promote SDL.