This study aimed to investigate the impact of perceived social support on the depression of postpartum women, and mainly focuses on confirming the mediator role of self-efficacy. A total of 427 new mothers from two general hospitals in Beijing accomplished the Multidimensional Scale of Perceived Social Support, General Self-efficacy Scale, and Edinburgh Postnatal Depression Scale. The results revealed that both social support and self-efficacy significantly correlate with postpartum depression. Structural equation modeling indicated that self-efficacy partially mediates the relationship between social support and postpartum depression.