Objective To explore the effects of indole-3-acetic acid (IAA) on metabolic dysfunction associated steatohepatitis (MASH) related liver fibrosis and its molecular mechanism. Methods A human-derived 3D liver spheroid was established and free fatty acid (FFA) was added to induce the MASH model. The spheroids were divided into five groups: control group, MASH group, low dose IAA group (FFA＋4 μmol/L IAA), medium dose IAA group (FFA＋20 μmol/L IAA) and high dose IAA group (FFA＋100 μmol/L IAA). Transforming growth factor-β1 (TGF-β1) was administrated to hepatic stellate cell lines LX-2. LX-2 cells were divided into four groups: control group, TGF-β1 group, medium dose IAA group (TGF-β1＋20 μmol/L IAA) and high dose IAA group (TGF-β1＋100 μmol/L IAA). Hematoxylin and eosin staining and Sirius red staining were performed to estimate pathological change. Immunofluorescence was performed to evaluate smooth muscle actin α (α-SMA), COL1A1, β-catenin level. Real-time quantitative reverse transcription polymerase chain reaction was performed to evaluate COL1A1, TGFB, CTNNB1, CCND1, MMP7, ACTA2 levels. Western blotting was performed to evaluate α-SMA and β-catenin level. CCK-8 was performed to evaluate cell proliferation. Wnt pathway agonist CHIR99021 was administrated in rescue experiments. Results FFA treatment successfully induced the MASH phenotype in 3D liver spheroids. Compared with the MASH group, the percentage of collagen area was reduced in all IAA dose groups (P＜0.05), and the expression levels of hepatic stellate cell activation markers α-SMA and COL1A1 were decreased (P＜0.05). In cell experiments, the expression of hepatic stellate cell activation-related genes (TGFB1, ACTA2, COL1A1) in medium dose and high dose IAA groups was lower than that in the TGF-β1 group (P＜0.05), and the cell proliferation level in the high dose IAA group was lower than that in the TGF-β1 group (P＜0.05). Compared with the TGF-β1 group, IAA downregulated β-catenin levels and inhibited the expression of downstream genes in the Wnt pathway (P＜0.05); activation of the Wnt pathway could partially reverse the effects of IAA. Conclusions IAA may inhibit the proliferation and activation of hepatic stellate cells by suppressing the Wnt/β-catenin signaling pathway and alleviate MASH-related liver fibrosis.