Background: Developmental care was introduced as a method to protect the neonates' neurological system; it consists of a large range of medical and nursing interventions that help to reduce the stress of neonates in neonatal units. Aim of the study: To assess factors affecting non-applicability of developmental supportive care by neonatal nurses at neonatal intensive care unit. Research design A descriptive research design was utilized. Setting: The study was conducted at the neonatal intensive care unit (NICU) at Tanta Educational Hospital at Gharbia Governorate. Subject: A purposive sample of sixty nurses who were providing direct care to neonates in the previously mentioned setting.. Tools for data collection: Two tools were used questionnaire sheet and observational checklists to identify the factors contribute to non-applicability of the developmental supportive care. Results: It was found that more than half of the studied nurses had poor knowledge and had incompetent level of practices as well as the lack of neonatal physical set up facilities, which all considered as factors lead to non-applicability of developmental supportive care. Conclusion: the deficit of knowledge, lack of neonatal physical set up facilities lead to non-compliance of nurses' practice, which considered factors contribute to non-applicability of developmental supportive care. Recommendation: Enhancing neonatal nurse's knowledge, practice and standardize the neonatal physical set up for application developmental supportive care.