This study aimed to examine the mediating effect of college satisfaction on the effect of career preparation behavior on first job satisfaction among college graduates, and to test for differences in this effect by the highest level of parental schooling attainment. Using data from 2019 Graduate Occupational Mobility Survey (2020), we conducted structural equation model analysis and multi-group analysis with the highest level of parental schooling for a total of 6,473 participants, and obtained the following results. First, college satisfaction fully mediated the effect of career preparation behaviors on first job satisfaction among college graduates. Differences in the relationship between college graduates’ career preparation behaviors and first job satisfaction were based on the highest level of parental schooling attainment. Specifically, college satisfaction did not mediate the effect of career preparation behaviors on first job satisfaction in the first-generation college students(FGCS) group, but fully mediated it in the continuing-generation college students(CGCS) group. In addition, the path difference between the two groups was significant only for the effect of career preparation behavior on college satisfaction. We concluded that higher education should be improved to enhance first job satisfaction in terms of career development based Labor Market Effectiveness, and empirical improvement measures and suggestions for follow-up studies were provided.