Abstract Background The predictive role of lactate in critically ill patients with acute upper gastrointestinal bleeding (UGIB) remains to be elucidated. Objective The primary objective of this study was to assess the value of lactate level on admission to predict in-hospital death in patients with UGIB admitted to the intensive care unit (ICU). The secondary objective was to assess whether lactate level adds predictive value to the clinical Rockall score in these patients. Methods This was a retrospective cohort study that included 133 patients with acute UGIB admitted to the ICU. Inclusion criteria were age > 18 years and presence of UGIB on admission to the ICU. Results Mean age was 55.4 years old and 64.7% were male. The most common cause of gastrointestinal bleeding was peptic ulcer disease, followed by erosive esophagitis/gastritis. The in-hospital mortality was 22.6%. Median lactate level in survivors and nonsurvivors was 2.0 (interquartile range IQR 1.2–4.2 mmol/L) and 8.8 (IQR 3.4–13.3 mmol/L; p < 0.01), respectively. The receiver operating characteristic (ROC) area to predict in-hospital death for clinical Rockall score and lactate level (0.82) was significantly higher than the ROC area for the clinical Rockall score alone (0.69) ( p  < 0.01). Conclusions In patients admitted to the ICU with acute UGIB, lactate level on admission has a high sensitivity but low specificity for predicting in-hospital death. Lactate level adds to the predictive value of the clinical Rockall score. Given its high sensitivity, lactate level can be used in addition to other prediction tools to predict outcomes in patients with UGIB.