Abstract Background: Given the pandemic crisis of COVID-19 infection and the controversy that surround the different lines of treatment which range from simple multivitamins to the very expensive antiviral drugs which at most of times lack the solid evidence of efficacy, many studies are needed to determine the influence of such myriad of this unlimited drugs and specifically to determine if this supplementary medicines -vitamins and minerals-does actually have a role in manage-ment of these patients or just represent unwanted polyphar-macy. This study is intended to determine the contribution of vitamin D deficiency to the severity of Covid-19 infection. Aim of Study: To determine the association between serum vitamin D level and the severity of covid-19 infection. Patients and Methods: A prospective study including eighty threepatients was conducted in Chest and Clinical Pathology Departments in Bab El-Sha'aria and Al-Hussin Hospitals, Al-Azhar University during the period from January 2021 to June 2021. Serum vitamin D3 level was assessed ineighty three patients with COVID-19 infection of variable severity, diagnosed based on the integrated clinical, laboratory, and CT chest radiological data. Results: This study include83patientswith mean age of 48.4±17.8 including 26 (31.3%) males and 57 (68.7%) females. Regarding the severity of covid-19 infection; 35 (42.2%) patients was suffering from non pneumonic Covid-19 infec-tion,mild pneumonic covid-19 infection was present in 11 (13.3%) patients, covid-19 pneumonia of moderate intensity was present in 18 (21.7%) patients and severe covid-19 pneumonia was present in 19 (22.9%) patients. As regard the vitamin D3 it was sufficient in 20 (24.1%) patients, insufficient in 37 (44.6%) patients and deficient in 26 (31.3%) patients. CRP ranges from 4 to 96 with mean of 23.3±22.9. Correlation between the serum level of vitamin D and the severity of covid-19 infection was done. Conclusion: This study conclude that there is no associ-ation between the severity of covid-19 infection and the serum level of vitamin D. But because ofits common insufficiency and deficiency among population and patients with covid-19 infection and its importance for the immune system and the modulation of inflammatory response, vitamin D could be given in the daily recommended doses as a supplementary measure, however further studies are warranted to determine if larger doses of vitamin D could alter the disease course of covid-19 infection.