Licochalcone B (LicB) is a flavonoid derived from the Chinese medicinal herb Glycyrrhiza uralensis Fisch. Several previous studies have demonstrated the wide range of pharmacological activities shown by LicB. In this study, we investigated the anticancer effects of LicB in osteosarcoma (OS) tumor cells and its underlying mechanisms. According to the Cell Counting Kit-8 (CCK8) analysis and 5-ethynil-2'-deoxyuridine (EdU) staining results, we found that LicB suppresses OS cells (MG-63 and U2OS) growth depending on its concentration. Furthermore, flow cytometry and Western blot revealed that LicB promoted autophagy and apoptosis in OS cells in a dose-dependent manner. LicB treatment not only decreased the levels of Bcl-2, p62, Caspase-3, and Ki67 protein in MG-63 and U2OS cell lines but also increased the levels of Cleaved Caspase-3, Beclin1, Bax, Atg7, and LC3B. Mechanistically, LicB induced cell apoptosis by promoting the apoptosis-related cleavage of Caspase-3, while suppressing the phosphatidylinositol 3-kinase (PI3K)/protein kinase B (AKT)/mammalian target of rapamycin (mTOR) pathway to induce autophagy. The present work is the first to illustrate that LicB can serve as a potential drug candidate for tumor treatment owing to its ability to enhance autophagy and apoptosis, and suppress OS proliferation by inactivating the PI3K/AKT/mTOR pathway.