The purpose of the study was to examine the mediating effects of learning flow between self-directed learning and online class adaptation of middle-school students. 244 middle-school students in Busan were surveyed using the Self-Directed Learning Scale, Learning Flow Scale and Online Class Adaptation Scale. Correlation analysis was conducted to examine the relationships among these variables. Hierarchical multiple regression analysis was conducted to test the mediating effects of learning flow. In conclusion from the results and discussions, there are positive correlations among self-directed learning, learning flow and online class adaptation. Learning flow operated as a mediating factor between the self-directed learning and online class adaptation. These results suggest the importance of psychological intervention to improve learning flow and self-directed learning that affect online class adaptation of middle-school students.