Abstract: Two new steroidal saponins, macrostemonoside A and D, were isolated from the bulbs of Allium macrostemon Bung (Chinese name as Xie hal), a Traditional Chinese Medicine used forthe treatment of myocardial infarction. Their structures were established as tigogenin-3-O-β-D-glu-copyranosyl (1→2) β-D-glucopyranosyl (1→3)-β-D-glucopyranosyl (1→4)- β-D-galactopyranoside(1) and tigogenin- 3-O-β-D-glucopyranosyl (1→2) β-D-glucopyranosyl (1→3) (6-O-acetyl-β-D-glu-copyranosyl) (1→4)- β-D-galactopyranoside (2) by spectral and chemical evidences. 1 showedremarkable inhibitory effect on rabbit platelet aggregation induced by ADP in vitro (IC₅₀=0.065mmol).