While previous research has shown that social class is positively correlated with career decision self-efficacy (CDSE), how this relationship develops is unclear. This study tested the mediating effect of career social support on the link between subjective social class and CDSE and the moderating role of birthplace in the mediation model. A survey was completed among 388 Chinese college students. The results revealed that subjective social class could positively predict CDSE via career social support. For urban students, subjective social class was positively related to career social support, and it was indirectly related to CDSE via career social support. For rural students, subjective social class was positively related to CDSE. Finally, the implications for career education and counseling in Chinese college students are discussed.