OBJECTIVE: Breast cancer is one of the most aggressive and pervasive cancers identified in females. Dexmedetomidine (Dex) is an efficient anesthetic used in surgery. Our study aimed to explore the role of Dex in the malignancy of breast cancer cells in vitro and in vivo. Further, we investigate the molecular mechanism involved in the function of Dex on breast cancer cells. MATERIALS AND METHODS: The methyl thiazolyl tetrazolium (MTT) assay was applied to detect cell proliferation. The migration and invasion capacity of MDA-MB-231 cells was tested by wound healing assay and transwell assay. Western blot analysis was performed to quantify the protein expression levels of α2-adrenoceptor and ERK. RESULTS: The proliferation, migration and invasion ability of MDA-MB-231 cells was gradually increased after treatment of Dex in a dose-dependent manner in vitro. In addition, Dex could significantly elevate the volume and weight of xenotransplant tumor in vivo. Furthermore, Dex up-regulated the protein level of α2-adrenoceptor and consistently enhanced the phosphorylation of ERK without changing the total level of it. Similarity, over-expression of α2-adrenoceptor via its agonist Clonidine could mimic the function of Dex on breast cancer. CONCLUSIONS: These data suggest that Dex could promote the proliferation, migration and invasion of breast cancer cells through the activation of α2B-adrenoceptor/ERK signaling.