As part of search for new biologically active substances from marine organism, we have isolated a glyecrol glycoside from the marine red alga Gracilaria verrucosa. The structure of the glycerol glycoside was elucidated as 2-O-${alpha}-_D$-galactopyranosylglycerol[floridoside(4)] on the basis of spectroscopic and physicochemical evidences.