Background: Polycystic ovary syndrome (PCOS) is one of the most common female endocrine disorders affecting the reproductive age group and is thought to be one of the leading cause of female infertility. Many patients with polycystic ovary syndrome (PCOS) also have features of the metabolic syndrome, including insulin resistance, obesity, and dyslipidemia. Vitamin D affects insulin and glucose metabolism, and a low vitamin D status maybe a risk factor for PCOS. Aim: To determine vitamin D status among the obese adolescent with Polycystic Ovary Syndrome (PCOS) and to compare the vitamin D level among obese and nonobese adolescent with PCOS. Methods: This cross sectional study was done at the out-patient department of Obstetrics and Gynecology in Bangabandhu Sheikh Mujib Medical University (BSMMU) during November 2017 to October 2018 but the patients enrollment was started after 16 July 2018. The study comprises of 80 adolescent girls diagnosed as PCOS according to Rotterdam criteria, in the age range of 9 to 18 years, out of which 50 obese adolescent girls was considered as group I and 30 non obese adolescent girls was considered as group II. The biochemical parameters measured in the study includes fasting blood sugar, fasting insulin level and serum 25-hydroxy vitamin D level. Serum 25 (OH) D level less than 20 ng/ml was classified as vitamin D deficiency. Results: In this study it was observed that maximum patients were vitamin D deficient in both groups. In group I, 76% and in group II, 60% were vitamin D deficient. Again in group I, 14% and 33.3% in group II were vitamin D insufficient. Only 10% in group I and 6.7% in group II were found to have sufficient level of vitamin D. The mean Vitamin D was found 18.25±5.51 ng/ml in group I and 19.66±5.21 ng/ml in group II. The mean difference of vitamin D level between two groups was statistically not significant. There is a negative significant correlation between vitamin D and BMI which indicates level of vitamin D decreases with increase of BMI of the participants. Conclusion: Vitamin D deficiency was predominant in both groups. Though the difference of vitamin D level was not significant between two groups but the mean level of vitamin D is lower in group I than in group II. There is a negative significant correlation between vitamin D and BMI which indicates that higher BMI levels were associated with lower vitamin D levels.