A process is disclosed for producing with good productivity a cross-linked polyaspartic acid resin having biodegradability and high water absorbency. The process features inclusion of one of the following steps: (a) a polysuccinimide, which has been brought into a dispersed state by a dispersant, and a cross-linking agent are reacted to produce the cross-linked polyaspartic acid resin; (b) imide rings of a cross-linked polysuccinimide are subjected to a hydrolysis reaction while controlling a swelling degree of a resulting gel, whereby the cross-linked polyaspartic acid resin is produced; and (c) a gel of a cross-linked polysuccinimide, which has been obtained by reacting a cross-linking agent to a solution of a polysuccinimide in an organic solvent, is disintegrated to subject imide rings of the cross-linked polysuccinimide to a hydrolysis reaction, so that the cross-linked polyaspartic acid resin is produced. The process may also include one or both of the following steps as needed: (d) a gel of the cross-linked polyaspartic acid resin is washed with water and/or a water-miscible organic solvent; and (e) the polysuccinimide is produced using a basic amino acid as a cross-linking agent.