Background Osteosarcoma (OS) is the most common malignant bone cancer with more metastasis and increased occurrence in children and teen-agers and being responsible for more number of morbidity and mortality worldwide. Objective The current exploration was planned study the in vitro anticancer actions of dieckol against human OS MG-63 cells via PI3K/AKT/mTOR signaling inhibition. Methodology The cytotoxicity of dieckol was scrutinized by MTT assay. Effects of dieckol on the ROS accumulation, apoptotic cell death, and MMP level in the MG-63 cells were studied by respective fluorescence staining assays. The levels of proliferative, inflammatory, and apoptotic markers in the dieckol treated MG-63 cells were scrutinized by marker specific kits. The expressions of PI3K, AKT, and mTOR was assayed by RT-PCR. Results The MTT assay revealed that the dieckol dose dependently prevented MG-63 cells viability and the IC50 was found at 15 µM. Dieckol treatment effectively reduced the MMP level and improved the ROS generation and apoptosis in MG-63 cells. Dieckol also regulated the proliferative (cyclin D1), inflammatory (COX-2, IL-6, TNF-α, and NF-κB), and apoptotic (caspase-3, Bax, Bcl-2) markers in the MG-63 cells. The PI3K/AKT/mTOR signaling in the MG-63 cells were effectively inhibited by the dieckol treatment. Conclusion In conclusion, our findings from this study recommends that the dieckol could be a talented anticancer candidate for the OS management in the future.