Background: Pneumonia remains one of the most common causes of hospitalization and is leading cause of morbidity and mortality. Some studies have reported a relationship between serum levels of vitamin D and an increased incidence of pneumonia. The aim of this work was to assess vitamin D in infants, toddlers and preschool children suffering from pneumonia and correlate its level with severity, duration of hospital stay and outcome. Methods: This cross-sectional study was conducted on 120 preschool children. They suffered from pneumonia and were admitted to the PICU and Pulmonology Unit, Children,s Hospital Zagazig University from July 2021 to June 2022. A complete clinical examination was performed with special concern for anthropometric measurements, a history of sun exposure,a history of Ca and vitamin D supplementation,a previous history of LRTIS,a duration of hospital stay, a chest examination, signs of respiratory distress, CBC, CRP, blood pH and vitamin D. Results: The study included 51 (42.5%) infants, 53(44.2%) toddlers and 16 (13.3%) preschool children. Their ages ranged from 6 to 56 months. Regarding of severity, 49.2% of patients had severe pneumonia and 50.8% had very severe pneumonia. Vitamin D was insufficient in 14.2%, deficient in 73.3% and severely deficient in 12.5% of the patients. There was a significant relationship between vitamin D and the severity of pneumonia, duration of hospital stay, need for PICU and outcome. Conclusion: The role of vitamin D in the severity of pneumonia, duration of hospital stay and outcomes in children between 6 and 60 months could be assured.