The mononuclear title complex, [Co(C(6)H(6)NO(6))(C(2)H(8)N(2))].3H(2)O, contains an octahedrally coordinated Co(III) atom. The N-(carboxymethyl)aspartate moiety is coordinated as a tetradentate ligand, providing an OONO-donor set and forming two trans five-membered chelate rings and one six-membered chelate ring. A seven-membered chelate ring is also formed, which consists of part of the six-membered chelate ring and part of one of the five-membered chelate rings. The crystal structure of the complex is stabilized by hydrogen bonds with three water molecules.