Objective To explore whether residual cholesterol (RC) can serve as an evaluation indicator for risk stratification and prognosis in the elderly patients with acute coronary syndrome (ACS). Methods This was a retrospective cohort observation study. The cohort included consecutive elderly ACS patients admitted to Chinese PLA General Hospital from March 2020 to March 2021. The baseline clinical data, laboratory examination data, and other data were collected through the electronic medical record system, and RC was calculated. The baseline Syntax score (bSS) and residual Syntax score (rSS) were analyzed through coronary angiography. All patients were followed up, with the endpoint being the occurrence of major adverse cardiovascular events (MACEs). A multivariate logistic regression model was used to analyze the risk factors of the occurrence of MACEs, the receiver operating characteristic (ROC) curve to evaluate the predictive value of different risk factors in the prognosis of ACS patients, and the Spearman correlation test to evaluate the association between RC and the severity of coronary artery. SPSS statistics R was used for statistical analysis. Data comparison between two groups was performed using t test, Kruskal-Wallis H test or χ² test depending on data type. Results Totally 740 elderly ACS patients were enrdled, of whom 84 (11.35%) had MACEs during the one-year follow-up. Multivariate logistic regression showed that after adjustment, low-density lipoprotein cholesterol (OR=0.998,95%CI 0.997-1.000; P=0.015) and RC (OR=0.135,95%CI 0.069-0.265; P<0.001) were independent risk factors for MACEs in the elderly ACS patients. The ROC curve analysis showed that LDL-C (AUC=0.754,95%CI 0.719-0.786) and RC (AUC=0.774,95%CI 0.740-0.805) had good predictive value for patients′ prognosis, and that the combination of them (AUC=0.868,95%CI 0.840-0.893) was more efficacious than each one alone (P<0.001). The correlation coefficient R² between RC and rSS was 0.46, indicating a positive correlation (P<0.05). Conclusion RC is positively correlated with the degree of coronary artery stenosis and is valuable in predicting MACEs in the elderly ACS patients.