Background: Vitamin D has been implicated in the pathogenesis of a lot of autoimmune diseases. While the roles of vitamin D in rheumatic arthritis in adult have been investigated, less is known about the role of vitamin D in juvenile idiopathic arthritis (JIA). Objectives: Evaluation of the level of serum 25(OH) vitamin D in patients with juvenile idiopathic arthritis and its relationship to the disease activity. Methods: This was a case-control study included 36 children who were divided into two equal groups of matched age and sex. The first group (case group) consisted of 18 patients with JIA. The second group (control group) consisted of 18 healthy children. 25(OH) vitamin D level is measured in both groups and its relation to disease manifestations and disease activity using JADAS 27 score was determined. Results: The mean value of vitamin D serum level was significantly lower in patients than in healthy control. There was a negative correlation between vitamin D level and both disease activity and number of joints affected among the studied patients. Conclusion: Serum vitamin D levels were reduced in children with JIA. In addition, there was a significant negative correlation between serum vitamin D levels and both the number of affected joints and the disease activity as measured by JADAS 27 score.