Dihydrotanshinone I (DI), a naturally occurring compound extracted from Salvia miltiorrhiza Bunge, has been reported to have cytotoxicity to a variety of tumor cells. In this study, we investigated its anti-angiogenic capacity in human umbilical vein endothelial cells. DI induced a potent cytotoxicity to human umbilical vein endothelial cells, with an IC(50) value of approximately 1.28 microg/ml. At 0.25-1 microg/ml, DI dose-dependently suppressed human umbilical vein endothelial cell migration, invasion, and tube formation detected by wound healing, Transwell invasion and Matrigel tube formation assays, respectively. Moreover, DI showed significant in vivo anti-angiogenic activity in chick embryo chorioallantoic membrane assay. DI induced a 61.1% inhibitory rate of microvessel density at 0.2 microg/egg. Taken together, our results showed that DI could inhibit angiogenesis through suppressing endothelial cell proliferation, migration, invasion and tube formation, indicating that DI has a potential to be developed as a novel anti-angiogenic agent.