The ethanolic extract derived from the whole plant of Pardoglossum cheirifolium was submitted to phytochemical investigation. A new pyrrolizidine alkaloid, 3 '-O-acetylleptanthine N-oxide (1), was isolated together with three known compounds of the same class, i.e., heliosupine N-oxide (2), heliosupine (3), and heliovicine (4). The structure of the new compound was elucidated after extensive mono- and bidimensional NMR experiments and confirmed by a MS experiment.