The effects of molecular weight (M.W.) and contents of sulfate group (D.S.) and 3,6-anhydro-l-galactose (aGal) on water-holding capacity (used as a main index of gelation) were investigated with modified agarose (AG) and agaropectin (AP) sulfates.In the case of AG with M.W. 3000~100,000, water-holding capacity increased as the M.W. and aGal content increased. On the other hand, the water-holding capacity of AP was influenced markedly by the D.S. value. From these findings, the effects of the above factors on water-holding capacity can be summarized as follows. 3,6-Anhydro-d-galactose ring formation was observed on alkali treatment of AP sulfate or agar.