A GD₃-type ganglioside molecular species, LMG-4 (1), has been obtained from the polar lipid fraction of the chloroform/methanol extract of the starfish Luidia maculata. The structure of this ganglioside has been determined on the basis of chemical and spectroscopic evidence to be 1-O-[(N-acetyl-α-D-neuraminosyl)-(2→8)-(N-acetyl-α-D-neuraminosyl)-(2→3)-β-D-galactopyranosyl-(1→4)-β-D-glucopyranosyl]-ceramide. The ceramide moiety was composed of heterogeneous 2-hydroxy fatty acid and phytosphingosine units. This is the first report on the isolation and structure elucidation of GD₃-type ganglioside from echinoderms. Moreover, 1 exhibited neuritogenic activity toward the rat pheochromocytoma PC12 cells in the presence of nerve growth factor.