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BACKGROUND Geiparvarin (GN) is a natural compound isolated from the leaves of Geijera parviflora and exhibits anticancer activity. Nevertheless, little is known about its anticancer mechanism and anti-osteosarcoma (OS) effects. AIM This study explored whether GN effectively inhibits the growth and metastasis of osteosarcoma (OS) through a series of in vitro and in vivo experiments. METHODS Cell proliferation was measured by colony formation and MTT assays, and cell invasion was detected by Transwell assay. Flow cytometry and caspase-3 activity assays were carried out to examine cell apoptosis, and western blot analysis was performed to assess protein expression. In the animal experiments, the changes in relevant indexes were determined by immunohistochemistry and tumor vessel imaging. RESULTS Animal experiments showed that GN treatment significantly inhibited the growth and lung metastasis of OS, accompanied by increased apoptosis. In addition, GN treatment notably diminished COX2 expression and angiogenesis in OS. Moreover, COX2 overexpression nullified GN-induced decline in angiogenesis, growth, and lung metastasis and increased apoptosis in OS. Of note, the body weight of mice was enhanced after GN treatment, and the pathological examination manifested that GN treatment did not cause any damage to major organs. CONCLUSION Our data indicated that GN might depress the growth, metastasis, and angiogenesis of OS by decreasing COX2 expression, suggesting GN is a favorable candidate drug for OS treatment without side effects. Hence, it can be concluded that geiparvarin inhibits OS progression by reducing COX2 expression.