A series of studies on the isolation and structure elucidation of glycosphingolipids from several starfish species have been performed in our laboratory. From Acanthaster planci, we have isolated and characterized six cerebrosides, two ceramide lactosides and five gangliosides. Continuing our previous studies, the isolation and characterization of the ceramide (aglycone part of the glycosphingolipids) were carried out. From the less polar fraction of the CHCl3/MeOH extract of the starfish A. planci, a ceramide molecular species AC-1 was isolated by normal-phase silica-gel column chromatography. AC-1 was separated by reversed-phase HPLC into thirteen fractions. Among them, three compounds (AC-1-6, AC-1-10, AC-1-11) were pure ceramides. The structures of these ceramides were determined on the basis of chemical and spectroscopic evidence (positive ion FABMS/MS, 1H and 13C NMR, etc.) as three new phytosphingosine-type ceramides: (2S,29R,3S,4R,9Z)-2-(2-hydroxyhexadecanoylamino)-9-docosene-1,3,4-triol (AC-1-6), (2S,29R,3S,4R)-2-(2-hydroxytricosanoylamino)hexadecane-1,3,4-triol (AC-1-10), and (2S,29R,3S,4R)-2-(2-hydroxytetracosanoylamino)hexadecane-1,3,4-triol (AC-1-11). To our knowledge, this has been the first time that ceramides from starfish have been isolated and characterized. AC-1-6, AC-1-10 and AC-1-11 are new ceramides, although AC-1-11 has been obtained as a synthetic product before.