Introduction: Acute rheumatic fever (ARF) is an autoimmune response to B hemolytic streptococcal pharyngitis infection. (1) Rheumatic heart disease (RHD), the permanent injury to the cardiac valves caused by ARF, is a major cause of morbidity and mortality in developing countries all over the globe. Vitamin D level has played a crucial role in the severity of mitral valve regurgitation because of its immunomodulatory effects. (2) Aim of the study: The study aims to assess the levels of vitamin D in pediatric RHD patients with mild to severe mitral valve regurgitation. Methods: Fifty adolescents with confirmed to have RHD and fifty matched healthy controls diagnosed by 2-Dimensional Transthoracic Echocardiography were recruited from Rheumatic Heart Disease Clinic at Cairo University Specialized, (EGYPT). Serum 25(OH)D concentrations were measured using dried blood spots and anthropometric measures were recorded to evaluate nutritional status. Logistic regression analysis was done to identify an association between vitamin D deficiency and the severity of Mitral regurgitation in RHD. Results: Prospective case control cohort study, recruited 50 pediatric patients from Rheumatic Heart Disease Clinic at Cairo University Specialized. The patients were prescribed long-acting penicillin (LAP) for RHD management. The mean age of RHD patients was12.6+/-2.51 years with a 2:1 female to male ratio (62% versus 38%; respectively). There was an inverse weak correlation between vitamin D serum level and the degree of regurgitation; however, the result wasn’t statistically significant. Vitamin D levels showed a statistically significant association with patients who were compliant to LAP. All laboratory measures showed no statistically significant differences between trivial to mild and moderate to severe mitral regurge cases except for calcium. Conclusion: Vitamin D can play a significant role in predicting severity of mitral valve regurgitation. Future studies are required in Egypt to further predict the other nutritional factors and demographic characteristics in pediatric patients with variable severity of RHD.