PURPOSE: The purpose of this study was to investigate the effects of the professional nurse's postpartum breast-feeding support on breast-feeding prevalence for mothers who delivered in Baby-Friendly Hospitals (BFH). METHODS: This quasi experimental study was designed with a nonequivalent control group post test. The subjects of this study were 55 mothers who were hospitalized in the delivery room of a university hospital which was selected as a BFH in Daegu from October 1, 2005 to June 30, 2006. Twenty nine mothers were assigned to the experimental group and 26 mothers to the control group. Postpartum breast-feeding support by nurses' telephone calls to the experimental group was provided once a week for 4 weeks postpartum and then once a month for 16 weeks postpartum. Four post tests were given at postpartum week 4, 8, 12, and 16. The control group was given a telephone call at postpartum week 4, 8, 12, and 16. RESULTS: The breastfeeding prevalence of the experimental group was significantly higher than that of the control group for each period. CONCLUSION: Postpartum breast-feeding support by nurses may be a useful intervention to increase breast-feeding prevalence.