Background/Aims:The search for noninvasive biomarkers that can efficiently estimate the extent of liver fibrosis progression is ongoing. Although Fibrosis-4 (FIB-4), the aspartate transaminase-to-platelet ratio index (APRI), and the Forns index have been reported as useful biomarkers, their investigation in autoimmune hepatitis (AIH) is limited. This study aimed to examine the usefulness of these serological indices and a newly developed index in predicting liver fibrosis progression in AIH.Methods:The study analyzed data from 190 patients diagnosed with AIH at our institution between 1990 and 2015. Their histological liver fibrosis progression and clinical long-term prognosis were evaluated retrospectively (cohort 1). In 90 patients, receiver operating characteristic (ROC) curves were compared to choose severe fibrosis cases with respect to existing indices (FIB-4, APRI, and Forns index) and the ferritin–zinc ratio (cohort 2).Results:In cohort 1, liver-related death and hepatocellular carcinoma rates were significantly higher in the severe (n = 27) than in the mild (n = 63) fibrosis group (p= 0.0001 and 0.0191, respectively). In cohort 2, liver-related death in the severe fibrosis group was significantly frequent (p= 0.0071), and their ferritin–zinc ratio was higher (median 2.41 vs. 0.62,p= 0.0011). ROC analyses were performed to compare the ability of the ferritin–zinc ratio, FIB-4, APRI, and the Forns index to predict severe and mild fibrosis. Accordingly, areas under the ROC were 0.732, 0.740, 0.721, and 0.729, respectively.Conclusions:The serum ferritin–zinc ratio can noninvasively predict liver fibrosis progression in AIH and be applied to predict long-term prognosis.