This study aimed to systematically review randomized clinical trials (RCTs) to clarify the effects of pro-/synbiotic supplementation on anthropometric and biochemical measurements in women with polycystic ovary syndrome (PCOS). PubMed, Scopus, ISI Web of Science, Cochrane Library, and Google Scholar were searched through September 2018. Eight RCTs (nine treatment arms) were included. Pro-/synbiotic supplementation significantly reduced fasting blood sugar (-2.52 mg/dl, 95% confidence interval (CI): -4.10 to -0.95), insulin (-2.27 µIU/mL, 95% CI: -3.40 to -1.14), homeostasis model assessment for insulin resistance index (-0.69, 95% CI: -0.98 to -0.40), C-reactive protein (-1.69 Hedges', 95% CI: -3.00 to -0.38), and total testosterone (-0.12 ng/mL, 95% CI: -0.17 to -0.08) in women with PCOS. However, changes in the mean difference of weight and body mass index did not reach a statistically significant level. The findings suggest that pro-/synbiotic supplementation may improve glucose homeostasis parameters, hormonal, and inflammatory indices in women with PCOS.