In the title compound, [Tb(CH(3)CN)(C(23)H(26)O(8))(H(2)O)(3)](ClO(4))(3), the Tb(3+) atom is eight-coordinated by one N atom of an acetonitrile molecule, three water O atoms and four ligand O atoms. The Tb(3+) atom is located on one side of the macrocycle and the carbonyl oxygen coordinated to the terbium [Tb1-O1= 2.210 (3) Å] is bent out of the xanthone plane by 0.514 (3) Å. The geometry around terbium is a distorted two-capped trigonal prism.