Purpose: This study aimed to develop and evaluate the effectiveness of an educational program on developmental positioning (EPDP) for nurses in neonatal intensive care units (NICUs).Methods: The study utilized a non-equivalent control group pretestposttest design. Sixty NICU nurses were recruited from two university hospitals in Daejeon, South Korea. The EPDP consisted of a 7-week program: 3 weeks of education and practice, followed by 4 weeks of encouragement messages using social networking services. Developmental positioning (DP) posters and DP aids were also provided during the intervention period. The intervention group (n=30) received the EPDP, but not the control group. The data were analyzed using the x2 test, the Fisher exact test, the independent t-test, and repeated-measures analysis of variance.Results: Participants' knowledge (t=7.49, p<.001), attitudes (t=1.99, p=.001), self-efficacy (t=2.99, p=.004), performance of DP (t=2.98, p=.004) and Infant Positioning Assessment Tool (IPAT) scores (F=29.50, p<.001) were significantly higher in the intervention group than in the control group.Conclusion: The EPDP can be an effective and useful program for improving the performance of DP among NICU nurses by increasing their knowledge, attitudes, and self-efficacy of DP. However, further research involving various NICU settings is needed to gather more empirical evidence.