BackgroundTriglyceride-glucose (TyG) index, a novel surrogate marker of insulin resistance, has been demonstrated to be significantly associated with cardiovascular disease. It remains indistinct regarding the association between TyG index and non-culprit coronary plaque characteristics in patients following acute coronary syndrome (ACS). MethodsThe present study retrospectively recruited patients who were diagnosed with ACS and underwent non-culprit optical coherence tomography (OCT) examination. The study population was divided into 2 groups based on the median of TyG index, which was calculated as Ln [fasting triglyceride (TG) (mg/dL) x fasting blood glucose (FBG) (mg/dL)/2]. The non-culprit plaque characteristics were determined by interpreting OCT images in accordance with the standard of previous consensus. Results110 patients (54.8 +/- 12.1 years, 24.5% female) with 284 non-culprit plaques were included in the current analysis. TyG index was closely associated with high-risk plaque characteristics. Elevated TyG index was consistent to be an independent indicator for thin-cap fibroatheroma (TCFA) [odds ratio (OR) for per 1-unit increase 4.940, 95% confidence interval (CI) 1.652-14.767, P = 0.004; OR for taking lower median as reference 2.747, 95% CI 1.234-7.994, P = 0.011] and ruptured plaque (OR for per 1-unit increase 7.065, 95% CI 1.910-26.133, P = 0.003; OR for taking lower median as reference 4.407, 95% CI 1.208-16.047, P = 0.025) in fully adjusted model. The predictive value of TyG index for TCFA and ruptured plaque was moderate-to-high, with the area under the receiver operating characteristic curve (AUC) of 0.754 and 0.699 respectively. The addition of TyG index into a baseline model exhibited an incremental effect on the predictive value for TCFA, manifested as an increased AUC (0.681, 95% CI 0.570-0.793 vs. 0.782, 95% CI 0.688-0.877, P = 0.042), and significant continuous net reclassification improvement (0.346, 95% CI 0.235-0.458, P < 0.001) and integrated discrimination improvement (0.221, 95% CI 0.017-0.425, P = 0.034). TyG index failed to play an incremental effect on predicting ruptured plaque. ConclusionTyG index, which is simply calculated from fasting TG and FBG, can be served as an important and independent risk predictor for high-risk non-culprit coronary plaques in patients following ACS.