A known monoalkyl glycerol ether, ($pm$)-1-nonadecyloxy-2,3-propanediol (1) was isolated from the ethyl acetate extract of a soft coral Dendronephthya gigantea as a weakly cytotoxic constituent against four human cancer cell lines, A549, HT-29, HT-1080, and SNU-638. In addition, a known ceramide, (28,3R,4E,8E)-N-hexadecanoyl-2-amino-4,8-octadecadiene-1 ,3-diol (2), was also isolated as an inactive constituent. This is the first report on the isolation of the compounds 1 and 2 from the octocoral, Dendronephthya species.