Background: Cancer-associated fibroblasts (CAFs) are vital components of gastric cancer (GC) microenvironments, which impact the aggressive characteristics of GC cells. The objective of this study is to evaluate the influence of High Mobility Group Box (HMGB) on CAF-related GC. Methods: The tissues of 10 GC patients who underwent surgery the Sanya Central Hospital of Hainan Province from July 2018 to July 2019 were collected for the clinical study. Moreover, the GC cell lines, including MGC-803, AGS, and SGC-7901, were used in vitro experiment. We investigated the molecular mechanism of the miR-200b/HMGB3 axis in affecting the chemoresistance and epithelial-mesenchymal transition (EMT) of GC cells induced by CAFs. Cell transfection, Cell Counting Kit-8 (CCK-8), Transwell assay, western blot, enzyme-linked immunosorbent assay (ELISA), and other experiments were employed.Results: We found that miR-200b was down-regulated, yet HMGB3 was up-regulated in CAF-related GC.The CAFs markedly promoted cisplatin (CDDP) resistance, proliferation, invasion, migration, and EMT of GC cells. Gain-assay of miR-200b demonstrated that miR-200b inhibited the HMGB3 release from CAFs.In-vivo experiments confirmed that the growth and EMT of GC cells co-cultured with CAF-miR-200b were significantly reduced. Furthermore, CAFs enhanced the activation of ERK, JNK, and the Wnt/β-catenin pathways, and those pathways, as well as the malignant behaviors of GC cells, were obviously attenuated by miR-200b or HMGB3 silencing.Conclusions: Collectively, HMGB3 derived from CAFs is negatively regulated by miR-200b and promotes the malignant behaviors of GC cells.