To obtain a biodegradable builder having excellent chelating capability and useful from economic viewpoint by graft-polymerizing a water-soluble ethylenic unsaturated monomer to a partially oxidized and modified group of a polysaccharide.

The objective builder is produced by the graft-polymerization of a water-soluble ethylenic unsaturated monomer[e.g. (meth)acrylic acid or maleic acid] to a partially oxidized and modified group of a polysaccharide (preferably starch or cellulose). The builder can be produced by reacting an aqueous solution or suspension of a polysaccharide with an oxidizing agent at 0-10°C for 1-48hr to effect the oxidization reaction, adding hydrogen peroxide and ascorbic acid to the obtained aqueous solution or suspension of the partially oxidized polysaccharide in the presence of a water-soluble ethylenic unsaturated monomer and reacting at 30-80°C for 1-6hr. The oxidizing agent is preferably a hypochlorous acid salt or periodic acid. The builder is compounded to a detergent composition preferably at a weight ratio (builder/surfactant) of 1/10 to 4/3.