〔Abstract〕 Objective To analyze the changes of Antithrombin Ⅲ(AT-Ⅲ) activity in patients with HBV-related acute liver failure(HBV-ACLF) and to study its potential correlation with liver function and coagulation function. Methods 80 subjects with HBV-ACLF and 48 subjects with chronic hepatitis B(CHB) as the controls were enrolled in our hospital. The level of AT-Ⅲ was detected with chromogenic substrate method, the relationships between AT-Ⅲ and total bilirubin(TBIL),albumin(ALB), alanine aminotransferase(ALT), aspartate aminotransferase(AST),prothrombin time activity(PTA), international normalized ratio of prothrombin time(PT-INR) and end-stage liver disease(MELD) score were analyzed by using Spearman rank correlation, and the receiver operating characteristic(ROC) curve was used to evaluate whether AT-Ⅲ could be used as a laboratory test to influence the clinical prognosis of HBV-ACLF. Results The activity level of AT-Ⅲ in patients with HBV-ACLF decreased than those of patients with CHB. Compared with CHB patients, other markers of liver function and coagulation function increased except for the decrease of ALB and PTA in patients with HBV-ACLF, and the differences were significant(P<0.05). The level of AT-Ⅲ activity was correlated with TBIL, PT-INR and PTA in patients with HBV-ACLF. And it was negatively correlated with MELD score in the prognosis of patients with HBV-ACLF. The ROC curve showed that the area under the curve predicted by AT-Ⅲ was 0.686, the sensitivity was 75.0%, the specificity was 52.9%, and the boundary value was 16.4%; the area under the curve predicted by MELD core was 0.698, the sensitivity was 76.5%, the specificity was 55.9%, and the boundary value was 28.5; the area under the curve predicted by MELD core and AT-Ⅲ was 0.756, the sensitivity was 62.5%, the specificity was 88.2%, the boundary value were 25 and 20.1%. Conclusion AT-Ⅲ is associated with the severity and progression of liver injury in patients with HBV-ACLF. The clinical combination of AT-Ⅲ and MELD score is useful in predicting the prognosis of HBV-ACLF.