Specific inhibition of angiogenesis has been considered a powerful strategy for the treatment of cancer and other angiogenesis-related human diseases. Hovenia dulcis Thunb., Japanese raisin tree or Oriental raisin tree, is a hardy tree found in Asia, Eastern China and Korea and has been known to possess various biological activities, including antifatigue, antidiabetic, neuroprotective and hepatoprotective activity. In the present study, for the first time, we evaluated whether a 100% ethanol extract of Hovenia dulcis Thunb. (HDT) inhibits the angiogenesis of human umbilical vein endothelial cells (HUVECs) using in vitro angiogenesis assays. HDT suppressed vascular endothelial growth factor (VEGF)-induced proliferation, migration, invasion and tube formation of HUVECs at subtoxic doses. In addition, HDT significantly inhibited in vivo angiogenesis of the chorioallantoic membrane from growing chick embryos without exhibiting cytotoxicity. Furthermore, HDT downregulated not only VEGF receptor 2 (VEGFR2) signaling in HUVECs, but also hypoxia-inducible factor (HIF)-1α expression in hepatocarcinoma cell line HepG2. Ampelopsin is a bioactive flavanonol found in Hovenia dulcis Thunb. Our data showed that ampelopsin inhibited angiogenesis with no cytotoxicity by suppressing both VEGFR2 signaling and HIF-1α expression. These results suggest that Hovenia dulcis Thunb. and its active compound ampelopsin exhibit potent antiangiogenic activities and therefore could be valuable for the prevention and treatment of angiogenesis-related diseases including cancer.