Background: Chronic Spontaneous Urticaria (CSU) is an allergic auto-immune disease with more than 6 weeks of continuous symptoms, it is known to trigger allergic wheal formations and angioedema. Vitamin D at optimal levels plays an important role in adjusting innate immunity thus People who has deficient or insufficient levels of serum vitamin D suffer from disturbance in immune system. Accordingly, studies have been established to explore the effect of vitamin D on CSU. Aim of the Study: To determine the effect of 12 weeks daily oral vitamin D supplementation [ high (4,000 IU/d) versus low (600 IU/d) dose of orally administered vitamin D3] on Urticaria activity score (UAS-7), quality of life (QOL) and medication burden in patients with chronic spontaneous urticaria, and to assess the relationship between vitamin D levels and CRP in these patients. Patients and methods: This single blind randomized prospective study conducted to 50 patients with CSU, admitted to Ain shams hospital, 50 patients were divided into 2 groups according to the dose of vitamin D orally administrated to these subjects, the first was group A , patients have received vitamin D orally in High dose 4000 IU/Day compared to group B , which included 25 cases received oral vitamin D in a low dose concentration 600 IU/d , Patients has been followed up in 3 times at baseline (0 week) , 6 weeks and 12 weeks intervals. Results:  Serum vitamin D levels in Group were higher than Group B (44.48 12.86 vs 34.45 5.43). Medication consumption was higher in group A compared to group B, thus favors orally low dose administration of vitamin D at first 6 weeks in the beginning of treatment course. UAS7 score in group A was better than Group B from baseline) to 6 weeks (P=0.009 vs 0.239) and from 6 weeks to 12 weeks. (P= 0.011 vs <0.0011). There was no significant difference in serum CRP between group A and group B as regards to CRP, furthermore there was no statistically correlation between 3 times intervals in group A and group B separately (12.71 1.47 vs 13.11 1.45). Conclusion: Improvement of both quality of life, and UAS7 score after receiving of High dose 4000 IU/d vitamin D orally in Group A, could benefit patients with CSU and decrease the complication of this disease. It was also found Serum Vitamin D level has no significant relation with C Reactive protein level, thus we couldn't relay on evaluation the chronicity of urticarial by measuring its value in serum blood with patients suffering from chronic spontaneous idiopathic urticaria.