We prepared a three-dimensional monometallic lanthanoid assembly, Na-5[Ho(THB4-)(2)]center dot 7H(2)O (THB = 1,2,4,5-tetrahydroxybenzene), that exhibits ferromagnetism with a Curie temperature of 11 K. Such a ferromagnetic ordering is due to the effective mediation of the magnetic interaction between Ho3+ ions by the THB4- ligand.