Background: To investigate the association between serum carbohydrate antigen 125 (CA125) and the presence as well as severity of diabetes retinopathy (DR) in Chinese adult patients with type 2 diabetes. Methods: A hospital-based cross-sectional study was conducted from February 2012 to November 2018. DR was assessed using Early Treatment Diabetic Retinopathy Study criteria. Vision-threatening DR (VTDR) was diagnosed if subjects had severe nonproliferative DR (NPDR), proliferative DR (PDR), or clinically significant macular edema (CSME). Multivariate logistic regression models were applied to explore the associations. Results: Among the 2696 participants, the overall prevalence of DR was 25.1%, of which the prevalence of mild NPDR, moderate NPDR, and VTDR was 10.8%, 4.5%, and 9.9%, respectively. Serum CA125 level was significantly higher in participants with DR and increased with the severity of DR (P = 0.013). After accounting for age, gender, smoking, drinking, duration of diabetes, anti-diabetic agents use, systolic blood pressure, pulse pressure, weight, hemoglobin A1c and fasting plasma glucose levels, CA125 level was significantly associated with subjects in any-severity DR