Abstract: Dehydrocorydaline (DHC) was shown to reduce the production of thromboxane B₂ (TXB₂)in platelets and 6-keto-prostaglandin F_1α (6-keto-PGF_1α in the aorta of rabbits in vitro. The effect of DHC increased with the increase of dose.DHC 0.41 mg was found to inhibit the formatiom of TXB₂ markedly while not reduce the content of 6-keto-FCF_1α. DHC also exhibited obvious inhibitory effect on the arachidonic acid (0.66mmol/L) induced formation of platelet malondialdehyde (MDA). These effects were similiar to the specific cycloxygenase inhibitor, aspirin (0.03 mg/ml). The results suggest that (1) DHC reduced both contents of TXA₂ and PGI₂ in vitro. (2) DHC markedly inhibited the system of cycloxygenase in cell microsomes. (3) As to whether TXA₂ synthetase or cycloxygenase was inhibited in these experiments is still to be elucidated.