Abstract : Systemic Lupus Erythematosus (SLE) in children has a degree of inflammation that must be observed. This can be assessed by a disease activity assessment score with a SLEDAI score. Patients with SLE have levels of 25 (OH)D which are low. To determine the relationship between 25-hydroxyvitamin D (25 (OH)D) levels with disease activity in the SLE as assessed by the SLEDAI score. This study was an observational analytic study with a cross-sectional design in children aged 5-18 years at H. Adam Malik General Hospital Medan from April to May 2019. The SLEDAI score and 25(OH)D level was assessed when the patient visited and was treated at the hospital. hospital. A total of 30 research subjects had met the inclusion criteria. As many as 93.3% were women with the most common age being 10-14 years. The 25 (OH) D level value was 14.9 ± 6.6. Disease activity in LES assessed by SLEDAI score was mostly found in high activity group patients with an average score of 11.7±8.9. The highest frequency of SLEDAI scores was in the kidney organ where 66.7% of the sample had hematuria, 60% had pyuria, 43.3% had cylindrical symptoms in the urine, and 23.3% had proteinuria. 25 (OH) D levels with SLEDAI scores had a negative correlation (r = -0.284, p> 0.05). There is no significant correlation between 25(OH)D level and SLE disease activity.