Adult stem cells, such as bone marrow mesenchymal stem cells (BMSCs), are postdevelopmental cells found in many bone tissues. They are capable of multipotent differentiation and have low immune-rejection characteristics. Hepatocytes may become inflamed and produce a large number of free radicals when affected by drugs, poisoning, or a viral infection. The excessive accumulation of free radicals in the extracellular matrix (ECM) eventually leads to liver fibrosis. This study aims to investigate the restorative effects of mouse bone marrow mesenchymal stem cells (mBMSCs) on thioacetamide (TAA)-induced damage in hepatocytes. An in vitro transwell co-culture system of HepG2 cells were co-cultured with mBMSCs. The effects of damage done to TAA-treated HepG2 cells were reflected in the overall cell survival, the expression of antioxidants (SOD1, GPX1, and CAT), the ECM (COL1A1 and MMP9), antiapoptosis characteristics (BCL2), and inflammation (TNF) genes. The majority of the damage done to HepG2 by TAA was significantly reduced when cells were co-cultured with mBMSCs. The signal transducer and activator of transcription 3 (STAT3) and its phosphorylated STAT3 (p-STAT3), as related to cell growth and survival, were detected in this study. The results show that STAT3 was significantly decreased in the TAA-treated HepG2 cells, but the STAT3 and p-STAT3 of HepG2 cells were significantly activated when the TAA-treated HepG2 co-cultured with mBMSCs. Strong expression of interleukin (Il6) messenger RNA in co-cultured mBMSCs/HepG2 indicated mBMSCs secret the cytokines IL-6, which promotes cell survival through downstream STAT3 activation and aid in the recovery of HepG2 cells damaged by TAA.