Background: Uterine fibroids, which are non-cancerous tumors found in the pelvic region, are prevalent among women of reproductive age. The incidence of uterine fibroids varies between 5.4% and 77%. These tumors develop within the muscular walls of the uterus in women who have not yet reached menopause. Symptomless or causing abnormal bleeding, pelvic pressure symptoms, infertility, and growth or regress throughout life, leiomyomas are more common in people of African descent, those who have never given birth, those who are overweight, and those with a positive family history of fibroids. Millions of women suffer with leiomyoma, and it is one of the most common reasons for hysterectomy. Aim of the Work: to determine whether or not vitamin D supplementation reduces the size of uterine fibroids in patients who are deficient in the nutrient. Patients and Methods: This RCT was a single-blind randomized study at tertiary care hospital at Beni-Suef university hospital from January 2022 till June 2022 and performed on a total of 100 women in childbearing period diagnosed with uterine fibroid who had vitamin- D deficiency. Results: As regards the fibroid size after Vitamin D supplementation for 6 months, according to the findings of this study, there is no statistically significant distinction in fibroid size amongst Vitamin D group and control group over the first three months whereas, fibroid size was substantially less in the Vitamin D group. At the fourth, fifth month and sixth months. Consequently, the size of the tumor decreased significantly over the six months in the group of Vitamin D supplementation with no significant improvement in the size of the fibroid over the 6 months in the control group. Conclusion: According to the results of the current research, vitamin D supplementation is an effective, low-risk method of preventing leiomyoma growth and stabilizing fibroids, therefore avoiding the onset of more serious and symptomatic disorders. Vitamin D supplementation seems to prevent fibroid growth.