Background & aims: There are conflicting results for the association of 25-hydroxyvitamin D [25(OH)D] with metabolic syndrome (MetS). The aim of this study was to investigate the relationship between serum 25(OH)D concentration and MetS and its components in a Chinese adult population. Methods: A cross-sectional study of 25,691 men and 22,146 women from China was performed in 2017. MetS was defined according to National Cholesterol Education Program Adult Treatment Panel III. Logistic and restricted cubic spline regression analyses were used to assess the association between 25(OH) D and MetS. Results: Of the 43,837 participants aged 18-96 years, the prevalence of MetS was 21.0%. The adjusted odds ratios (ORs) for MetS decreased gradually with increasing 25(OH)D concentrations (P for trend < 0.001). Compared with the lowest 25(OH)D quartile, the adjusted ORs (95% CIs) for MetS from second to the highest quartile were 0.95 (0.88-1.02), 0.82 (0.76-0.88), and 0.70 (0.65-0.75), respectively. We observed a linear dose-response relationship between 25(OH)D concentrations and MetS risk (P for nonlinear trend = 0.35); the risk of MetS decreased by 20% (OR = 0.80, 95%CI: 0.77-0.82) for each 10 ng/ml increment in 25(OH)D concentration. The inverse association was more evident in men and participants with eGFR <60 ml/min/1.73 m2 or AST >40 U/L (all P for interaction < 0.05). Moreover, significant inverse relationships were observed between 25(OH)D and elevated triglycerides, reduced high-density lipoprotein cholesterol and elevated blood pressure. Conclusions: These findings suggested that higher 25(OH)D concentrations were independently associated with a dose-response decreased risk of MetS among Chinese adults. (c) 2021 Elsevier Ltd and European Society for Clinical Nutrition and Metabolism. All rights reserved.