Starch, agarose, κ-carrageenan and porphyran were sulfated by sulfuric acid with dicyclohexylcarbodiimide as a condensation reagent. In all the cases, the sulfation at O-6 appeared to be predominant on the basis of results from methylation analyses. Although the reactivities of the other hydroxyl groups towards the present sulfation reaction were less than that at C-6, they varied depending on the position in the sugar residue of the polysaccharides. The sulfated agarose was further fractionated in terms of the difference in the solubility of its cetylpyridinium salt to KCl solution. The major fraction resembled the main polysaccharide of funoran (agarose 6-sulfate) on the basis of the behavior of its cetylpyridinium salt,13C NMR measurements and methylation analyses.