In our continuing research on biologically-active glycosphingolipids from echinoderms, a series of studies on the isolation, structure elucidation and biological activities of the glycosphingolipids from the sea cucumber species have been performed in our laboratory. In continuation of the preceding studies on the sea cucumber Holothuria pervicax, the isolation and characterization of the biologically active glycosphingolipids from the sea cucumber Stichopus japonicus (Manamako in Japanese) has been conducted to develop novel medicinal resources from marine natural products. In this paper, we report the isolation and the characterization of a ganglioside molecular species SJG-1 from the body walls of S. japonicus. The n-hexane soluble lipid fraction, obtained from the chloroform/methanol extract of the body walls of S. japonicus, was subjected to reversed-phase followed by normal-phase column chromatography to give a ganglioside molecular species SJG-1, which appeared as a single spot on normal-phase TLC. A ganglioside molecular species SJG-1 has been obtained from the n-hexane soluble lipid fraction of the chloroform/methanol extract of the sea cucumber Stichopus japonicus. On the basis of chemical and spectroscopic evidence, the structure of SJG-1 has been determined. SJG-1 possesses N-glycolylneuraminic acid (sialic acid), nonhydroxy fatty acids and phytosphingosine-type long-chain bases as major ceramide components. The ganglioside SJG-1 exhibits neuritogenic activity toward the rat pheochromocytoma cell line PC12 cells in the presence of NGF.