The water extracts from red seaweeds Laurencia obtusa and Laurencia filiformis comprise complex sulfatedagarans. Those from L. obtusa have 3-linked -d-galactose units in part sulfated on 2-position or meth-ylated on 6-position, while the 4-linked units are mostly 3,6-anhydro- -l-galactose and -l-galactose6-sulfate, some of the latter units are substituted with -d-xylose on 3-position, precluding alkalinecyclization. The 3-linked -d-galactose units of the agarans from L. filiformis are mostly sulfated on 2-position, but approximately half of these residues also carry the 4,6-O-(1-carboxyethylidene) group. The4-linked 3,6-anhydro- -l-galactose units are methylated or substituted in part with single stubs of -d-xylose on 2-position. This is the first time that substitution with xylose of 3,6-anhydro- -l-galactoseis reported. Besides, -l-galactose 2-sulfate carrying single stubs of -d-xylose on 3-position was alsodetected. These galactans have some common structural characteristics with those of other species ofthis genus, but also others that are specific for these species.FONACIT proyecto nro. 2012000830