Background <p>Low-grade chronic inflammation is observed in women with polycystic ovary syndrome (PCOS). A recent genome-wide association study (GWAS) suggested that several inflammation marker levels were altered in the blood routine tests in PCOS patients and such changes were associated with variant gene clusters. Therefore, inflammatory marker alterations in the blood routine tests are significant and might be involved in the onset as well as progression of PCOS. Compared with other markers, these inflammatory markers in the blood routine tests are less expensive and easier to detect. Very few studies have evaluated the changes in platelet indicators like platelet count and mean platelet volume (MPV) in Chinese women with PCOS. The aim of the study was to investigate the changes in platelet-related inflammatory indices in Chinese women with PCOS.</p> Methods <p>The study included 299 women aged 18–47 with PCOS and 481 healthy women as the control group. We conducted propensity score matching to refine our dataset, utilizing the ‘Matching’ package in R to match cases with the disease to controls. Correlation analyses were performed using Pearson correlation analysis. Partial correlation analysis was used to analyse the correlation between MPV and the indicators after adjusting for age, body mass index (BMI) and waist circumference (WC). Binary logistic regression (forward-wald) was used to evaluate if the relationship between MPV and PCOS was independent of obesity, insulin resistance (IR), and hyperandrogenism.</p> Results <p>After matching the age, BMI, and WC of the two groups, high-sensitivity CRP (hs-CRP), white blood cell counts (WBCs), lymphocytes, platelets and great platelet count (GPC) were significantly higher (<i>P</i> = 0.007, 0.022, 0.011, 0.014, and 0.000, respectively), and mean platelet volume (MPV) and platelet distribution width (PDW) were significantly lower in PCOS patients compared with the control group (<i>P</i> = 0.000, 0.016, respectively). Neutrophils, neutrophil-to-lymphocyte ratio (NLR), and platelet hematocrit (PCT) did not show statistically significant differences between the two groups (<i>P</i> = 0.196, 0.480, 0.646, respectively). Decreased MPV was independently associated with the occurrence of PCOS (<i>P</i> = 0.005, OR = 0.770, 95% CI, 0.641–0.925). MPV was negatively correlated with total testosterone (TT), free testosterone (FT) and total cholesterol (CHOL) levels after correcting for age and obesity (<i>r</i> = -0.149, <i>P</i> = 0.000; <i>r</i> = -0.093, <i>P</i> = 0.010; <i>r</i> = -0.081, <i>P</i> = 0.025; respectively).</p> Conclusions <p>Chinese PCOS patients have significantly reduced MPV as an inflammatory indicator independent of obesity, IR, and dyslipidemia.</p>