This systematic review aims to evaluate all epidemiological evidence in the literature linking the effect of vitamin D supplementation to metabolic and hormonal functions in women with polycystic ovary syndrome. The literature search was performed with two databases, namely Medline/PubMed and Web of Science, until 20 May 2019 for both observational and experimental studies concerning relationships between vitamin D and polycystic ovary syndrome. A total of ten studies with randomized, double-blinded, and placebo-controlled trial design from 2008 to 2019 were selected for this review. The inclusion criteria were women 18-45 years of age with polycystic ovary syndrome and comparing the metabolic or endocrine parameters between placebo and vitamin D supplementation groups. A total of ten studies were selected for this review. We found that vitamin D supplementation had a significant effect on insulin metabolism, total serum testosterone, hirsutism, C-reactive protein, and total antioxidant capacity in women with polycystic ovary syndrome. Evidence from available randomized controlled trials suggests that patients with polycystic ovary syndrome should take vitamin D supplementation for the beneficial effect of metabolic profiles. However, future research is needed regarding the beneficial effects in women who are non-obese with polycystic ovary syndrome, as well as more studies with larger sample sizes.