Background: Prematurity and related problems, especially respiratory distress syndrome, are one of the main challenges for neonatal medicine. Many studies have shown the relationship between lung development and vitamin D. Objective: To investigate Vitamin D status and to evaluate the effect of vitamin D supplement as adjuvant therapy in the management of respiratory distress syndrome (RDS) in preterm infants. Patients and Methods: This study included 90 preterm neonates chosen from those at NICU of Minya General Hospital and Al-Azhar University, Assiut, Egypt. The cases were divided into two main groups; a group with RDS (case group 66 cases) and a group without RDS (control group =24 cases). The group with RDS was further subdivided into three subgroups (subgroup I received just traditional therapy and the subgroup II received traditional therapy plus vitamin D 400 IU/day, while subgroup III received traditional therapy plus vitamin D 800 IU/day). Results: The RDS group had lower neonatal and maternal vitamin D concentrations than the group without RDS. We found a strong positive correlation between neonatal and maternal vitamin D levels on the day of delivery. The subgroups supplemented with vitamin D had a significant improvement in all ABG parameters, lower Downs score, less hospital stay, less morbidity than the subgroup without vitamin D supplementation. Conclusion: Administration of vitamin D as adjuvant therapy in cases of RDS was associated with a significant decrease in severity, rate of complications, and duration of hospital stay in the subgroup received 800 IU/Day compared to the subgroup received 400 IU/Day.