Abstract: Ligustrazine is one of the active constituents extracted from ligusticam wallichii Franch, a tranditional Chinese medicine used to invigorate blood circulation and to remove blood stasis. Its structure is tetramethyl pyrazine. This compound has been used in the treatment of acute cerebrovascular ischemia disease and angina pectoris with beneficial effects. We investigated the effect of ligustrazine on human platelet strips with Salganicoff's method and showed that ligustrazine relaxed the tension of contracting platelet strip, inhibited the contractile response to ADP, arachidonic acid and TXA₂ analogue SQ26655. The concentration of Ligustrazinc required to relax 50% of the maximal effect was found to be 160 μg/ml in K-H solution with 1 mM Ca²⁺. The level of cAMP in ligustrazine treated platelet was nearly one-fold more as control. The effect of ligustrazine on relaxation of platelet strips was dose-dependent but not on the increase of cAMP. After using adenylate cyclase inhibitor SO 22536, ligustrazine inhibited the contractile response to calcium ionophore A23187. This result suggests that ligustrazine may inhibit the. tension of platelet strip by inhibiting Ca²⁺ in cytoplasm.