Abstract: Berberine(Ber)20 mg· kg^-1·d^-1for l,3, or 5 d inhibited plateletaggregation induced by ADP, arachidonic acid (AA) and collagen(Coll) in rats with 24 h reversiblemiddle cerebral artery occlusion (MCAO) , and the platelet adhesiveness was inhibited as well. Usingradioimmunoassay method, the thromboxane B₂ (TXB₂ ) and 6-keto-prostaglandin Fla(6-keto-PGF_la)contents in rat plasma were measured 24 h after MCAO. The results indicate that the TXB2 levels afterdrug treatment were lower than those in ischemia control rats, but the 6-keto-PGFlalevels showed noobvious difference between the two groups. The same dose of Ber was also shown to inhibit thrombosisformation. This suggests that the decline of platelet aggregation and decrease of TXB₂ content may beone of the important factors involved in the anti-cerebral ischemia effect of Ber.