Objective: The Korean Triage and Acuity Scale (KTAS) is a triage tool for patients in the emergency department (ED). This study aimed to evaluate the ability of the KTAS to predict poor outcomes in South Korean ED patients with a suspected infection. We also compared the effectiveness of KTAS with that of the National Early Warning Score (NEWS) and Modified Early Warning Score (MEWS) in predicting poor outcomes. Methods: We conducted a single-center retrospective study that included adult patients with a suspected infection who were admitted to the ED between January 2019 and December 2019. Patients who received a prescription for antibiotics and associated culture tests in the ED were considered to have an infection. Poor outcomes were evaluated by in-hospital mortality, general ward admission, and intensive care unit (ICU) admission. A receiver operating characteristics (ROC) curve analysis was performed to evaluate and compare KTAS, NEWS, and MEWS. Results: Of the 4,127 patients in the study, in-hospital mortality was reported in 154 (3.7%) patients. The median KTAS was lower in the non-survivors than in the survivors (2.51 vs. 3.35). Multivariate logistic regression analysis showed that the KTAS was associated with in-hospital mortality, ward admission, and ICU admission. The area under the ROC curve (AUROC) values for predicting in-hospital mortality associated with the KTAS, NEWS, and MEWS were 0.776 (95% confidence interval, 0.747-0.803), 0.829 (0.759-0.811) and 0.739 (0.694-0.786), respectively. Conclusion Our results showed that the KTAS was associated with in-hospital mortality, ward admissions, and ICU admissions among ED patients with a suspected infection. Thus, KTAS may be reliable in predicting a poor outcome in ED patients with a suspected infection.