A copolymer resin composition provided by the process of the present invention is of considerable strength and moldability and is produced by polymerization of a monosaccharide or a polysaccharide that is derived from natural objects and has a hydroxyl group, and a carboxyl group or a salt thereof with a compound having a hydroxyl group and a carboxyl group. The monosaccharide or the polysaccharide serves as a polyfunctional central compound. The copolymer resin composition is obtained through dehydration-polycondensation of (A) at least one selected from the group consisting of a monosaccharide and a polysaccharide having a hydroxyl group, and a carboxyl group or an ion-exchanged carboxyl group; and (B) at least one selected from the group consisting of (b1) hydroxycarboxylic acid, (b2) polyhydroxycarboxylic acid, (b3) a mixture of an aliphatic polyol and an aliphatic polybasic acid, and (b4) an aliphatic polyester obtained by the reaction of an aliphatic polyol with an aliphatic polybasic acid. Preferably, alginic acid is used to serve as the monosaccharide or the polysaccharide having a hydroxyl group and a carboxyl group.