Background: Acute-on-chronic liver failure (ACLF) is associated with high mortality, but transplantation improves survival. Optimizing organ function is time-consuming and can increase infection risk. This study investigated the optimal pretransplant waiting period. Methods: In this retrospective study of patients with ACLF who underwent transplantation between January 2021 and August 2024, perioperative details and morbidity were compared between survival and mortality groups. Receiver operating characteristic (ROC) analysis was used to determine the cutoff for the pretransplant waiting period. Results: Among 112 patients with ACLF under the European Association for the Study of the Liver criteria, 61 (54.5%) underwent living donor liver transplantation (mean age, 41 years; 51 males [83.6%]). The most common etiology was viral infection (44.2%). The median Chronic Liver Failure Consortium (CLIF-C) score was 44 (respiratory failure, 14.7%; renal failure, 16.4%). There were 14 (22.9%) posttransplant deaths. The median waiting period between admission and surgery was longer in the mortality group (8 vs.4 days, P=0.2). The area under the ROC curve for the optimal pretransplant waiting period was 0.723 (P=0.01). A cutoff of 5 days predicted mortality with 71.4% sensitivity and 61.9% specificity. On univariate analysis, survivors and nonsurvivors differed significantly in age, hemoglobin level, warm ischemia time, and postoperative gastrointestinal (GI) bleeding; on multivariate analysis, postoperative GI bleeding independently predicted mortality. During a median follow-up of 17 months, no deaths occurred. Conclusions A pretransplant waiting period of 5 days predicted mortality; furthermore, postoperative GI bleeding was an independent predictor of mortality. Further studies are required to confirm these findings.