BACKGROUND: Hepatocellular carcinoma (HCC) is often characterized by poor prognosis, high invasiveness and chemotherapeutic resistance, and its migration is strongly dependent on the specific tumor microenvironment. Fibroblasts, such as cancer-associated stromal fibroblasts (CAFs), are the main supporting cells in the tumor microenvironment. Thus, an understanding of how these cells communicate is required for HCC treatment. METHODS: CAFs and paracancerous fibroblasts (PAFs) were isolated from patients' surgical specimens, followed by exosome isolation and miRNA sequencing. The expression levels of miR-29b in different cell groups were detected by qPCR assay. Cell transfection with exogenous miRNAs was used to study whether the stromal cells could transfer miRNAs to HCC cells. Based on the preliminary results, a miR-29b mimic, inhibitor or miR-nonspecific mimic (miR-NSM) was further transfected into HepG2 and Huh7 cells prior to scratch wound healing and cell invasion experiments. Finally, the transfected cells were stained with Hoechst 33348. RESULTS: The direct transfer of miR-29b from CAFs to HCC cells through an exosome was observed in this study. DNA methyltransferase 3b (DNMT3b) expression was directly inhibited by miR-29b, while metastasis suppressor 1 (MTSS1) expression was upregulated in HCC cells. Such changes further induced growth arrest and inhibited HCC cell invasion. CONCLUSIONS: Exosomal miR-29b from CAFs can play a crucial role in the development, progression and metastasis of HCC. By functioning as a tumor suppressor that targets DNMT3b, miR-29b may serve as a potential therapeutic agent.