Natural intoxication of livestock by the ingestion of Ipomoea carnea (Convolvulaceae) sometimes occurs in tropical regions of the world. Polyhydroxylated alkaloids were isolated from the leaves, flowers, and seeds of the poisonous plant and characterized. Chromatographic separation of the leaf extract resulted in the isolation of swainsonine (1), 2-epi-lentiginosine (2), calystegines B1 (3), B2 (4), B3 (5), and C1 (6), and N-methyl-trans-4-hydroxy-l-proline (7). The contents of 1 in the fresh leaves and flowers were 0.0029 and 0.0028%, respectively, whereas the contents of 1, 3, and 4 in the seeds were ∼10 times higher than those in the leaves and flowers. Alkaloids 3, 4, and 6 showed a potent inhibitory activity toward rat lysosomal β-glucosidase, with IC50 values of 2.1, 0.75, and 0.84 μM, respectively, and alkaloid 5 was a moderate inhibitor of α- and β-mannosidases. Although alkaloid 1 is known as a powerful inhibitor of lysosomal α-mannosidase (IC50 = 0.02 μM), alkaloid 2, which has been thought to be an intermediate in the biosynthesis of 1, was also a potent inhibitor of α-mannosidase with an IC50 value of 4.6 μM.