Developmental care is a strategy used in neonatal intensive care units (NICUs) to help reduce the amount of stress that a newborn infant is exposed to. Developmental care helps NICUs to be more "baby friendly”. The aim of the current study was to examine the effect of developmentally supportive care training program on nurses' performance during tub bath provided for neonates in NICU, and to explore the effect of developmentally supportive care training program on behavioral responses of newborn infants during tub bath in NICU. The study adopts a quasi-experimental research design. The study was conducted in the NICU at Benha Specialized Pediatric Hospital. The data were collected using structured interview sheet, newborn assessment sheet, Neonatal Behavioral Assessment Scale developed by Brazleton and Nugent (1973) and an observational checklist to evaluate the nurses’ performance during tub bath. Apparently, the study results evident that there was highly statistically significance differences between the means of the total scores of nurses’ performance regarding tub bath for newborn infants before and after application of developmentally supportive care program (DSC). Moreover, the means of NBAS items were all significantly improved among newborn infants and they exhibited less stress and greater comfort during tub bath after application of DSC program. The study recommended that collaboration and continuing education of the staff in the NICU are vital to improve the quality of care provided for newborn infants.