Background: Nurses must possess the necessary knowledge, competent practices, and positive attitude about preterm neonates' developmental supportive care, to effectively implementing this care model. Aim: Evaluate the effect of developmental supportive care program for preterm neonates on nurses' performance. Design: One group pretest-posttest quasi-experimental research design was adopted. Sample: A convenient sample of forty nurses who were providing care for preterm neonates. Tools: A structured interview questionnaire, observational checklists and Likert scale of nurses' attitude. Results: Most of nurses had unsatisfactory total score of knowledge in pretest, improved to most and less than two thirds of nurses had satisfactory (excellent total score) of knowledge in posttest and follow-up respectively, four fifths of nurses had incompetent total score of practice in pretest, improved to more than three quarters and less than two thirds of nurses to be competent in posttest and follow-up respectively. Highly statistically significant improvements were detected regarding the total mean scores of nurses' attitude between pre, post and follow-up. Conclusion: The developmental supportive care program had a positive effect on improvement of the total mean score of nurses' knowledge, practice and attitude with highly statistically significant differences. Recommendation: Ensure regular on job training programs for nurses about developmental supportive care to update their performance.