Type1 diabetes mellitus is accounting for around 10% of all cases of diabetes mellitus. Insulin production is hampered by vitamin D insufficiency, which leads to glucose intolerance. The goal of the trial was to see if vitamin D intake had an effect on HbA1c in children with type 1 diabetes and vitamin D deficiency. In 56 patients with type 1 diabetes mellitus, a prospective non-blind, non-randomized clinical investigation was done. Between January 2021 and June 2021, these patients were recruited through Tobruck Medical Center's Diabetes Clinic. We assessed blood Vit D, Ca, and HbA1c in diabetic children with type I DM who had not previously received vitamin D, and then measured it again after 12 weeks of vitamin D delivery. We divided the youngsters into two groups: baseline before vitamin D administration and follow-up after 12 weeks of vitamin D administration. After 12 weeks of vitamin D administration, we noticed a significant improvement in HbA1c. As a result, with a p-value of ‹0.005, there is a significant strong association between vitamin D supplementation and HbA1c level in type I diabetic children. After vitamin D administration, we saw dramatic control and a decrease in HbA1c.