This invention provides a vascular protecting agent having salt-absorption inhibitory activity with the use of alginate oligosaccharide salt absorbed by the body via degradation to an oligosaccharide, so that a patient can easily and safely ingest such agent on a routine basis. A vascular protecting agent having salt-absorption inhibitory activity comprises, as an active ingredient, alginate oligosaccharide obtained by treating sodium alginate with a Pseudoalteromonas microorganism or a processed product thereof and/or a salt thereof.
