Purpose: This study was to develop a breastfeeding promotion program and to test effects of the program on levels of breast discomfort, breast size, sodium in breast milk, and type of feeding in mothers with breast engorgement following cesarean birth. Methods: A non-synchronized non-equivalent control group pretest-posttest design was used in this study. The participants were 70 postpartum mothers who were admitted to a postpartum care center and experienced breast engorgement following cesarean birth. The planned nursing intervention was the breastfeeding promotion program consisting of breast massage and 1:1 breastfeeding education, counseling, and support focusing on individualized problem solving provided for 10 days. Fifty-three women completed the program (experimental group 26, control group, 27). Measurements were level of breast discomfort, breast size, sodium in breast milk and type of feeding at pre and posttest. Results: Women who participated in the program experienced lower scores for breast discomfort, greater decrease in breast size, lower levels of sodium in breast milk, and practiced breastfeeding more than those in the control group. Conclusion: Results indicate that this breastfeeding promotion program is effective in reducing breast engorgement and improving breastfeeding practices, and is therefore recommended to enhance breastfeeding promotion practice in postpartum care centers.