This study aims to analyze the factors influencing changes in career maturity during one's transition from high school to entering college. The results from the analysis using the KELS 2005 dataset were as follows. First, the career maturity significantly increased as students entered college, when other variables were controlled. Second, as subcategories of the career maturity, planning ability, self-understanding, and career behavior improved by year. But there was no significant change in the attitude toward a job. Third, career maturity was affected by career education experiences, students' relationships with teachers, reading, and student participation in school activities. In conclusion, it is suggested that support from the schools and communities as well as individual efforts is essential for improving career maturity.