Objective To explore the effects and mechanisms of dexmedetomidine (Dex) on the biological behavior of osteosarcoma (OS) cells.Methods hFOB1.19 cells were used as reference, and human osteosarcoma cells MG63 and 143B were studied. The effects of Dex on the proliferation activity and cytotoxicity of MG63 and 143B cells were detected by MTT assay to determine the optimal exposure concentration of Dex. The experiment was randomly divided into control group and Dex exposure group. The effects of Dex on apoptosis, invasion and clonogenesis of MG63 and 143B cells were detected by flow cytometry, transwell chamber and clonal formation assay, respectively. In addition, α2-AR(Atipamezole), PKA(H892HCl) and ERK1/2(Ravoxertinib) inhibitors were pretreated to further explore the molecular mechanism of Dex affecting the biological behavior of MG63 and 143B cells. Results 25 nM Dex was the best concentration to promote the proliferation of MG63 and 143B cells. After exposure to 25 nM Dex, apoptosis of MG63 and 143B cells was decreased, cell invasion and clonal formation were enhanced, and the expression of p-ERK1/2 protein and the ratio of p-ERK1/2/ERK1/2 were up-regulated in MG63 and 143B cells. After pretreatment with ERK1/2 inhibitors, the effects of Dex on the biological behavior of MG63 and 143B cells were significantly reversed.Conclusion Dex promotes the proliferation, invasion, and clone formation ability of OS cells through the imidazoline I2/ERK1/2 signaling pathway, and inhibits OS cell apoptosis