Several studies have found that lactate correlates with surgical outcomes in patients with heart disease. However, the prognostic value of postoperative lactate in patients with acute type A aortic dissection (AAAD) remains unclear. This study aimed to investigate the relationship between postoperative lactate and in-hospital mortality in patients with AAAD. Patients who underwent AAAD surgery at Fujian Cardiac Medical Center from February 2020 to January 2022 were enrolled in this retrospective study. Correlations between in-hospital mortality and various parameters, including lactate, were investigated. A total of 357 patients were included in this study, 58 of which died. Multivariate logistic regression analysis revealed that body mass index (BMI) (odds ratio [OR] = 1.099, 95% confidence interval [CI]: 1.017-1.188, P = 0.017), cardiopulmonary bypass (CPB) time (OR = 1.005; 95% CI: 1.000-1.010, P = 0.039), and lactate (OR = 1.291, 95% CI: 1.182-1.409, P < 0.001) were independent risk factors for in-hospital mortality in AAAD patients. Receiver operating characteristic (ROC) curve analysis showed that lactate had a moderate power for in-hospital mortality (area under the curve [AUC] = 0.729, 95% CI: 0.647-0.810, P < 0.001). Furthermore, the combination of lactate, BMI, and CPB time showed better performance (AUC = 0.780; 95% CI: 0.706-0.854, P < 0.001) in predicting in-hospital mortality than in using these variables independently. Among patients undergoing AAAD surgery, postoperative lactate was significantly associated with in-hospital mortality. Lactate can be used as a potential predictor of in-hospital mortality. The combination of lactate, BMI, and CPB time showed better performance in predicting in-hospital mortality than using single one.