Triglyceride-glucose (TyG) index, a simple surrogate marker for insulin resistance (IR), has been reported as an independent predictor of arterial structural damage and future cardiovascular events. The association between TyG index and endothelial dysfunction remains uncertain.The purpose of this study was to investigate the association between TyG index and endothelial dysfunction.Endothelial dysfunction was measured using flow-mediated dilation (FMD). A total of 840 subjects, who voluntarily accepted FMD measurement at the Health Management Department of Xuanwu Hospital from October 2016 to January 2020, were included in this study. TyG index was calculated as Ln [fasting triglyceride (TG)(mg/dL) × fasting plasma glucose (FPG) (mg/dL)/2].The mean age was 59.92 ± 10.28 years and 559 (66.55%) participants were male. The TyG index was correlated with FMD values (P = 0.022). Each unit increment in TyG index was associated with lower FMD values (β = -0.330, 95%CI -0.609 to -0.052, P = 0.020) after adjusting for covariates. Age (β = -0.069, 95%CI -0.088 to -0.051, P < 0.001), female (β = 0.592, 95%CI 0.172 to1.012, P = 0.006), smoking (β = -0.430, 95%CI -0.859 to -0.002, P = 0.049) and hypertension (β = -0.741, 95%CI -1.117 to -0.365, P < 0.001) were also independent predictors for endothelial dysfunction. A significant association between the TyG index and endothelial dysfunction was found only in populations younger than 60 years (β = -0.843, 95%CI -1.371 to -0.316, P = 0.002), females (β = -0.612, 95%CI -1.147 to -0.077, P = 0.025), and populations without diabetes mellitus (DM) (β = -0.594, 95%CI -1.042 to -0.147, P = 0.009).Subjects with an elevated TyG index are more likely to have endothelial dysfunction, particularly in populations without DM.© 2024. The Author(s), under exclusive licence to Springer Science+Business Media, LLC, part of Springer Nature.