A new cage-type alkaloid, asparagamine A (1), was isolated from the 75% EtOH extracts of the dried roots of Asparagus racemosus Willd. (Liliaceae) by silica gel chromatography. Its molecular formula was confirmed as C₂₂H₂₇NO₅ by high-resolution electron impact mass spectrometry (HR-EI-MS). The relative stereostructure was elucidated by spectroscopic (IR, UV, NMR, 2D-NMR), chemical (N-oxidation) and single crystal X-ray analyses as a novel polycyclic pyrrolizidine derivative. In vitro assays showed that asparagamine A in doses of 10 to 100 µg/ml exhibited dose-dependent anti-tumor activity on several tumor models. To our knowledge, asparagamine A is the first example of a complicated polycyclic structure fused with a pyrrolizidine ring, which is extremely unique and interesting from the biosynthetic and pharmacological points of view.