The methanol extract of Viscum album var. coloratum, Korean mistletoe, showed potent prolongation effects on the bleeding time in rats in vivo, and whole blood clotting time and plasma recalcification time in rats ex vivo. The prolongation effect on the bleeding time of Korean mistletoe is comparable to that of Viscum album L., European mistletoe, 185.6% and 176.5%, respectively. However, the water extracts of the both plants did not show any prolongation effects. Platelet activating factor (PAF) receptor binding assay was carried out to elucidate the action mechanisms of the extracts, and both of the methanol extracts did not show any inhibitory activity. The $LD_{50}$ of the methanol extracts of both mistletoes are more than 2 g/kg. These results suggest that the mehtanol extract of Korean mistletoe might be a potential candidate to develop new drug to improve microcirculation.