Background: The triglyceride–glucose (TyG) index was shown to be an independent predictor of coronary artery disease (CAD) progression and prognosis. However, whether the TyG index can predict the severity of CAD in nondiabetic patients with chronic coronary syndrome remains unclear. Methods: A total of 118 individuals who underwent elective coronary angiography were classified into group A (59 with coronary lesions) and group B (59 with normal coronary arteries; as a control group) after coronary angiography and laboratory tests for fasting and the postprandial (PP) TyG index. The complexity of CAD was determined by the Synergy Between Percutaneous Coronary Intervention (SYNTAX) score (SYNTAX score >22 indicated moderate–high risk), and patients diagnosed with diabetes or prediabetes were excluded. Results: The TyG index was not related to the SYNTAX score in groups A and B; however, in the CAD group with an low-density lipoprotein (LDL) concentration <70 mg/dL (group A1), a fasting TyG index ≥8.25 and a PP TyG index ≥11 could predict moderate–high SYNTAX risk score; in addition, the odds ratio (OR) was 4.3× higher and the relative risk (RR) was 1.8× greater (OR = 4.3, RR = 1.8, 95% confidence interval = 1.4–13.5, P < 0.05) for individuals with a higher fasting TyG index ≥8.25 to have a moderate– high SYNTAX risk score. Individuals with a higher PP TyG index ≥11 had OR of 2.6× higher and a RR of 1.4× greater to have moderate–high SYNTAX risk score. Conclusions: Both fasting and PP TyG levels were associated with greater coronary anatomical complexity (SYNTAX score >22) in nondiabetic chronic coronary patients with LDL <70 mg/dL. Fasting and the PP TyG indices can serve as noninvasive predictors of CAD complexity in nondiabetic patients with LDL <70 mg/dL and could change the management and therapeutic approaches. Key Words: chronic coronary syndrome, diabetes mellitus, insulin resistance, prediabetes, SYNTAX score, triglyceride, triglyceride–glucose index