Background Osteosarcoma (OS) is an extremely aggressive primary bone cancer (BC) malignancy. A variety of malignancies can develop in the bones, including BC. Primary BCs are tumors that start in the bone. Bones can also become affected by tumors that start in the body’s organs or other tissues. Objectives Several reports suggested that corilagin (CL) exerts anticancer properties on various kinds of tumor cells; however, its molecular action on OS cells remains undefined. Materials and Methods The CL activity of OS cells’ cytotoxicity, intracellular reactive oxygen species (ROS), mitochondrial membrane potential (MMP), apoptosis, and cell-cycle distribution was evaluated by 3-[4,5-dimethylthiazol-2-yl]-2,5 diphenyl tetrazolium bromide (MTT) assay, dichloro-dihydro-fluorescein diacetate (DCFH-DA), Rh-123, acridine orange and ethidium bromide (AO/EB), 4′,6-diamidino-2-phenylindole (DAPI), and flow cytometry analysis. Results Results revealed that CL could suppress OS cell proliferation via enhanced intracellular ROS, and MMP loss, and triggered apoptosis in a dose-dependent has an inferior manner. Our findings demonstrated that CL alleviates U2OS and MG-63 cell proliferation by the ROS-mediated apoptosis, which triggers G0/G1 cell-cycle arrest. Conclusion Thus, CL might be a protective therapeutic agent against BC.