Breastfeeding knowledge, intention, and self-efficacy affect breastfeeding rates during the postpartum period. Insufficient knowledge, lack of intention, and poor breastfeeding self-efficacy reduce the likelihood of breastfeeding postpartum. The purposes of this study were to (1) assess women’s intention to breastfeed and knowledge and self-efficacy regarding breastfeeding following childbirth, and to (2) identify the factors associated with postpartum breastfeeding during women’s hospital stays. This longitudinal study with a pretest and posttest design study recruited pregnant women from the gynecology and obstetrics outpatient departments and inpatient wards at a medical center in northern Taiwan. Demographic and obstetric characteristics were recorded, and participants were assessed using the Numeric Rating Scale, the Breastfeeding Knowledge Questionnaire, the Breastfeeding Self-Efficacy Scale—Short Form, and breastfeeding status postpartum. Of the 120 participants, 25% reported breastfeeding during the postpartum hospital stay. Postpartum breastfeeding was associated with lower levels of education and higher prenatal levels of breastfeeding intention. Establishing a breastfeeding-friendly environment in the family and workplace may effectively increase continued breastfeeding.