Abstract: Neferine (Nef), a hypotensive agent with antiarrythmic action, is a dibenzyl isoquinoline alkaloid isolated from a Chinese medicinal herb(Nelumbo nucifera Gaertn). Its effects on platelet aggregation and TXA₂/PGI₂ and cAMP/cGMP balance were studied with methods of turbidimetry and RIA. Nef was shown to significantly inhibit rabbit platelet aggregation induced by ADP, collagen, arachidonic acid (AA) and platelet-activating factor(PAF) with IC₅₀ of 16, 22, 193 and 103 μmol·L^-1 , respectively. Nef was found to increase vascular 6-keto-PGF_1α and platelet cAMP levels in dose dependent manner, but inhibit AA stimulated TXA₂ release from platelets. Nef showed no significant effect on the platelet cGMP level. The results suggest that the mechanism of Nef on platelet aggregation is related to regulation of TXA₂/PGI₂ and cAMP/cGMP balance.