Purpose: Developmental care has been recognized as a very important component for the development and health promotion of preterm infants. However, research on how to assess developmental nursing competency has not been studied as expected. This study was done to develop and evaluate a new scale to measure nursing competency for developmental support of preterm infants. Methods: Concept analysis was done with using the Hybrid model of Schwartz-Barcott and Kim (2000), from which a preliminary new scale (30 items) was developed. To test the validity and reliability of the new scale being developed, data were collected from 122 NICU nurses at 4 hospitals in 3 cities in the Republic of Korea, from December, 2014 to March, 2015. Results: The final version of the Developmental Support Competency Scale for Nurses (DSCS-N) caring for premature infants was a 4-point Likert type scale, consisting of 19 items, and categorized as 6 factors, explaining 62.5% of the total variance. Each of the factors were named as follows; ‘environmental support’ (4 items), ‘parental support’ (3 items), ‘interaction’ (3 items), ‘critical thinking’ (3 items), ‘professional development’ (3 items), and ‘partnership’ (3 items). The Cronbach’s α coefficient for the scale was .83 and the reliability of the subscales ranged from .60~.76. Conclusion: The psychometric evaluation of the new scale demonstrated an acceptable validity and reliability. Findings indicate that the DSCS-N can be used as the tool to test the effect of educational programs for nurses and contribute to advance developmental care for preterm infant