ObjectiveTo examine the effectiveness of breastfeeding education and peer support groups organized by International Board Certified Lactation Consultants (IBCLCs) during the first week (T1) and the fifth to sixth week postpartum (T2), in terms of breastfeeding self-efficacy and exclusive breastfeeding rate. DesignA quasi-experimental design. SettingA maternity ward of a medical center in northern Taiwan. Participants214 postpartum women. InterventionThe control group (n = 122) received standard care, while the intervention group (n = 92) received standard care and attended a support group at T1 and T2. MeasurementsOutcome measures were assessed through self-administered questionnaires: Breastfeeding Self-Efficacy Scale-Short Form (BSES-SF) and exclusive breastfeeding rate. Demographic and obstetric data were collected from participants and from their medical records. A general estimating equation, t-tests, and chi-square tests were adopted to examine hypotheses. FindingsBefore examining the hypotheses, homogeneous tests confirmed the equality between the groups at T1. There were significant differences in breastfeeding self-efficacy (B = 0.21, p < 0.01) between the two groups from T1 to T2. The breastfeeding self-efficacy of participants in the intervention group was significantly higher than those in the control group (t = 3.26, p = 0.01) at T2. The exclusive breastfeeding rate (61%) in the intervention group at T2 was significantly higher than the rate (39%) in the control group (chi-square=11.28, p = 0.001). Key ConclusionsAttending IBCLC-organized breastfeeding education and support groups during early postpartum hospitalization may increase mothers’ breastfeeding self-efficacy and exclusive breastfeeding rate.