Background: Osteosarcoma (OS) is the most prevalent primary malignant bone tumor among adolescents, yet the efficacy of current medications is limited by a lack of understanding of the molecular mechanisms underpinning OS growth and metastasis. In previous studies, cantharidin (CTD), an effective component found in several clinical traditional Chinese medicine formulations, has demonstrated promising pharmacological efficacy against various malignancies. However, the precise biological functions and regulatory mechanisms of CTD in OS, particularly its interaction with the Forkhead box O3A (FOXO3A)/Methyltransferase Like 14 (METTL14)/Type III Intermediate Filament Protein (Vimentin) pathway, remain incompletely understood, warranting further investigation. Methods: Eighteen female BALB/c nude mice (four-week-old; 15 +/- 2 g) were utilized in this study and divided into three groups (n = 6/group): Normal control, Control, and CTD groups. Mice in the Normal control group received saline injections, while those in the other groups were injected with U-2 OS cells at the proximal end of the left tibia to establish an osteosarcoma model. Following successful model establishment, mice in the Control group received a daily intraperitoneal injection of saline (1 mg/kg), while those in the CTD group received an intraperitoneal injection of CTD (2.5 mg/kg). The inhibitory effect of CTD on tumor growth was evaluated after 28 days of continuous treatment. Additionally, the effects of CTD on OS cells were assessed using a Cell Counting Kit-8 (CCK-8), colony formation, and Transwell assays. Western blotting and quantitative real-time PCR (qRTPCR) were employed to quantify FOXO3A/METTL14 expression levels. Results: Lower levels of FOXO3A expression were observed in OS tissues (p < 0.01), with these expression levels significantly correlating with OS patient prognosis (p < 0.01). Compared to controls, CTD significantly suppressed osteosarcoma cell growth and metastasis as well as tumor growth (p < 0.001) by activating the FOXO3A/METTL14 pathway, consequently downregulating Vimentin expression (p < 0.001). Conclusion: Our findings indicate that cantharidin restricts osteosarcoma cell proliferation and metastasis through modulation of the FOXO3A/METTL14/Vimentin pathway.