Osteosarcoma (OS) is a rare malignancy of bone associated with poor clinical outcomes. The antitumor effects of GANT61 on OS is unclear. To investigate antitumor effects and mechanism of GANT61 in OS cells and xenograft model. Effects of GANT61 on cell viability, clone formation, cell cycle, apoptosis, migration, and invasion ability of OS cells were assessed. Reactive oxygen species (ROS) levels measured by dichlorofluorescein fluorescence were used to evaluate oxidative stress. The Xenograft model was constructed to investigate the antitumor effects of GANT61 in vivo. The microRNA (miRNA)‐1286 was downregulated, while RAB31 upregulated in OS tissues and cells. GANT61 inhibited viability, migration, and invasion ability of OS cells (SaOS‐2 and U2OS), and induced apoptosis and the ROS production, along with miRNA‐1286 upregulation and RAB13 downregulation. After knockdown of miRNA‐1286, GANT6‐induced cell inhibition was attenuated, along with RAB31 upregulation. Inversely, miRNA‐1286 overexpression downregulated RAB31. Dual‐luciferase reporter assay verified that miR‐1286 negatively targeted RAB13. Moreover, the knockdown of RAB31 stimulated apoptosis and ROS production while inhibited viability, migration, and invasion of GANT61‐treated cells. In vivo experiments further confirmed that GANT61 inhibited tumor growth and RAB13 expression, but enhanced miRNA‐1286. The study demonstrated that GANT61 inhibited cell aggressive phenotype and tumor growth by inducing oxidative stress through the miRNA‐1286/RAB31 axis. Our findings provided a potential antitumor agent for the OS clinical treatment.