Phytochemical study on the EtOAc extract of the seed of Erythrina addisoniae (Leguminosae) resulted in the isolation of a new erythrinan alkaloid, erysovine-N-oxide (1), along with eight known alkaloids, erysosalvinone (2), erysodine (3), 1H-indole-3-propanamide (4), glucoerysodine (5), erysotrine (6), erysovine (7), erythraline (8) and erysopine (9). Their chemical structures were identified on the basis of physicochemical and spectroscopic analyses.