The purpose of this study was to identify the factors influencing adolescents' career development. Using three-wave longitudinal data (Seoul Education Longitudinal Study2010), we examined the direct and indirect effects of parents' support on career maturity, in addition to the mediating effect of self-esteem in the relationship between parents' support and career maturity. We also examined the sex differences in the relationship among the variables. The subjects of this research were 4,187 adolescents who progressed from seventh grade in 2010 to ninth grade in 2012. The results are as follows: First, parental support has differential effects on career maturity via self-esteem. Second, in the longitudinal relationship of parents' support, self-esteem, and career maturity, the developmental differences according to sex were supported empirically. This study finding suggests that it is possible to enhance adolescents' career development by proper interventions in the period of adolescence which take into consideration these sex differences.