Background: Pelvic organ prolapse refers to protrusion of the pelvic organ into or out of the vaginal canal. In Bangladesh, 15.6% women suffered from pelvic organ prolapse and more than 11% of women require surgical correction of prolapse in their lifetimes. The pelvic floor is a unique part of the body and the function of which is dependent on interrelationship between muscle, nerve, connective tissue and bone. Pelvic organ prolapses results when these relationships are disrupted or there is weakness. Objective: The aim of the study was to evaluate the Vitamin D deficiency in postmenopausal women with pelvic organ prolapse. Methods: It was a cross sectional comparative study, done in the Department of Obstetrics and Gynecology of Bangabandhu Sheikh Mujib Medical University (BSMMU) to investigate the level of vitamin D in patients with and without pelvic organ prolapse to explore the association of vitamin D with pelvic organ prolapse. After taking informed written consent the serum vitamin D level of all participants was measured by CMIA technology with flexible assay protocols at Biochemistry and Molecular Biology department of the same institute. Statistical analysis of the results was obtained by using window-based computer software devised with Statistical Packages for Social Sciences (SPSS-24). Results: The study population was divided into two groups, a case group (n=74) consisting of patients with pelvic organ prolapse and a control group (n=74) comprising of women without pelvic organ prolapse. A total 148 participants of 52 years or older attending the out or inpatient department were enrolled in the study. Mean±SD level of Vitamin D in the case group was 13.96±5.18 ng/ml and in the control, group was 21.08±5.77 ng/ml respectively. The difference was statistically significant (p<0.05). Moreover, the vitamin D levels were inversely proportionate with the severity of pelvic organ prolapse. Conclusion: It can be concluded that women having low level of vitamin D have more chance of developing pelvic organ prolapse.