Purpose: This study examined the effects of breastfeeding education among preterm mothers. Methods: A nonequivalent control group, repeated measure, quasi-experimental study design was used. The participants comprised 46 preterm mothers recruited from the neonatal intensive care unit of a university hospital who were divided into two groups: 23 in the control group and 22 in the experimental group. The breastfeeding education program intervention to promote preterm mothers' self-efficacy used was devised based on the self-efficacy theory. The intervention program consisted of individual breastfeeding education with demonstrations and discharge education, and telephone follow-up education within one week after being discharged. The participants were surveyed before and after the intervention, and four weeks after being discharged from the newborn intensive care unit. Results: The intervention group showed a significant increase in breastfeeding self-efficacy compared with the control group (F=6.92, p=.003) and showed a significant increase in their breastfeeding attitude score (F=3.49, p=.039). Four weeks after discharge, the breastmilk volume of the intervention group increased significantly (t=-2.87, p=.006), and the same group continued to breastfeed more compared with the control group (χ2=4.50, p=.049). Conclusion: This study suggests that the preterm breastfeeding program had a positive effect on breastfeeding self-efficacy, breastfeeding attitude, and extending the breastfeeding period among preterm mothers.