Abstract: In this paper, the synthesis of leonurine (Ⅰ) and a series of syringic acid aminoesters (Ⅲ_1～12, Ⅳ_1～8) is reported.These compounds showed inhibitory activity against rat platelet aggregation induced by adenosine diphosphate or collagen in vitro. Compounds Ⅲ₁, Ⅲ₅ and Ⅳ₈ were more effective than leonurine. But, δ-guanidino-butanol-1(11) and syringic acid showed little activity.