Abstract: AIM: To study the inhibitory effects of triacetylshikimic acid (TSA) on rat platelet aggregation and its mechanism. METHODS: Light transmission was used to measure platelet aggregation. Methods of spectrophotometry and radioimmunoassay were used to measure the levels of malondialdehyde(MDA), thromboxane B₂(TXB₂), 6-keto-PGF_1α, cAMP and cGMP.RESULTS: TSA 12.5, 25,50,100 and 200 mg.kg^-1.d^-1 ig for 3 d inhibited the rat platelet aggregation induced by ADP and collagen. TSA 12.5, 50 and 200 mg.kg^-1 markedly increased the cAMP level and exhibited no effect on the cGMP level in rat platelets. TSA 200 mg.kg^-1 was shown to slightly inhibit AA-induced MDA generation and ADP-induced TXB₂ formation in rat platelets, and to slightly suppress 6-keto-PGF_1α generation from the abdominal aortae. CONCLUSION: TSA was found to be a potent inhibitor of platelet aggregation, which was partially concerned with the elevation of cAMP in platelets.