Abstract：【Objective】This study was conducted to examine the effects of dexmedetomidine on the proliferation and angiogenesis of MHCC97H and SMCC7721 human hepatocellular carcinoma（HCC）cell lines cultured in hypoxia condition in vitro，and investigated the possible mechanism involved.【Methods】MHCC97H and SMCC7721 human HCC cell lines under hypoxia culture condition were treated with presence or absence of dexmedetomidine（100 μmol/L）. Cell viability，colony formation，vasculogenic mimicry（VM） formation were assessed. The effects of dexmedetomidine on α-2A adrenergic receptor（α2A），hypoxia induced factor -1a（HIF- 1a），and vascular endothelial growth factor（VEGF）protein expression were evaluated with Western blot analysis.【Results】Cell proliferation assay and colony formation assay indicated that hypoxia obviously promoted the proliferation of MHCC97H and SMCC7721 cells（CoCl2 group vs corresponding control group，the proliferation rate of MHCC97H and SMCC7721：Day 3，142.2% and 133.8 %；Day 4，134.7 % and 131.0 %；Day 5，133.5 % and 136.2 %；all P < 0.05），and VM formation assay suggested that hypoxia increased angiogenesis of MHCC97H and SMCC7721 cells. Whereas dexmedetomidine significantly inhibited the proliferation（Dex+CoCl2 group vs CoCl2 group，the proliferation rate of MHCC97H and SMCC7721：Day 3，55.7% vs 60.7%；Day 4，46.9% vs 58.1%；Day 5，46.4% vs 57.0%，all P < 0.05）and angiogenesis of MHCC97H，SMCC7721 cells induced by hypoxia. Dexmedetomidine may exert these functions by activating α-2A adrenergic receptor，causing an decrease in HIF-1a and VEGF protein，while hypoxia activated HIF-1a and VEGF protein to promote the growth and angiogenesis of cells.【Conclusion】The findings provide evidence that hypoxia could promote the proliferation and angiogenesis of MHCC97H and SMCC7721 cells，while dexmedetomidine might inhibit these effects by down-regulating HIF-1a and VEGF protein expression through activating α-2A adrenergic receptor.