A new ganglioside molecular species, HPG-7 (1) was obtained from the polar fraction of the chloroform/methanol extract of the sea cucumber, Holothuria pervicax. On the basis of chemical and spectroscopic evidence, the structure of 1 was determined, and the major component was 1-O-[α-L-fucopyranosyl-(1→4)-(N-aceryl-α-D-neuraminosyl)-(2→11)-(N-glycolyl-α-D-neuraminosyl)-(2→4)-(N-acetyl-α-D-neuraminosyl)-(2→6)-β-D-glucopyranosyl]-(2S, 3S, 4R)-2-[(2R)-2-hydroxytetracosanoylamino]-14-methyl-hexadecane-1, 3, 4-triol. This is the first report on the isolation and structure elucidation of trisialo-ganglioside from sea cucumber. 1 showed neuritogenic activity toward the rat pheochromocytoma cell line, PC-12 cell.