BACKGROUND: The aspartate aminotransferase to alanine aminotransferase ratio (AAR) was seldom applied for fibrosis assessment in primary biliary cirrhosis (PBC) patients. GOALS: To validate the AAR for evaluating hepatic fibrosis, disease severity, and prognosis in patients with PBC. STUDY: Ninety-two consecutive PBC patients were retrospectively evaluated to validate the AAR for assessing the severity of liver function, the degrees of hepatic fibrosis, and predicting outcomes. RESULTS: AAR showed modest correlations to Mayo score, model for end-stage liver disease score, and Child-Pugh score (r=0.156, P<0.001; r=0.084, P=0.005; r=0.142, P<0.001, respectively) in evaluating the severity of liver function. For 46 patients who underwent liver biopsy, 35 were in early stage fibrosis and the other 11 were in advanced fibrosis. AAR was significantly higher in patients with advanced fibrosis than those with early fibrosis (mean±standard deviation; 1.40±0.44 vs. 0.98±0.65, P=0.001). The AAR yielded the highest area under the receiver operating curve of 0.847 than Mayo score, model for end-stage liver disease score, and Child-Pugh score in predicting advanced fibrosis. During a median follow-up of 44.5 months, 24 patients expired and 68 patients were alive. Patients with an AAR of 1 or less had significantly better prognosis than their counterparts (P=0.043). CONCLUSIONS: AAR is a simple and reliable marker to assess liver function and hepatic fibrosis as well as to predict outcomes in PBC patients.