To evaluate anti-aggregatory activity of traditional prescriptions and medicines for treatment of Ohyul symptom, 70% methanol extracts were examined using collagen stimulated in vitro platelet aggregation by impedance method in rat whole blood. The crude extracts from DoHaekSeungKiTang, BoYangHwanOhTang, Caesalpinia sappan, Rhus verniciflua, Rheum palmatum, Polygonum cuspidatum, Salvia miltiorrhiza were found to inhibit platelet aggregation. The effective crude extracts of traditional medicine were fractionated to dichloromethane, ethyl acetate, butanol and aqueous layer. Polygonum cuspidatum, Caesalpinia sappan aud Rhus verniciflua ethyl acetate fractions concentration-dependently $(250-50{mu}m/ml)$ inhibited the aggregation of platelet in whole blood induced by collagen. These results suggested that ethyl acetate fractions of Polygonum cuspidatum, Caesalpinia sappan and Rhus verniciflua have potent anti-aggregatory activity.