The title compound, [Fe(C(10)H(15))(2)][Ni(C(3)OS(4))(2)].C(4)H(8)O or [Fe(Cp*)(2)][Ni(dmio)(2)] x THF, where [Fe(Cp*)(2)](+) is the decamethylferrocenium cation, dmio is the 2-oxo-1,3-dithiole-4,5-dithiolate dianion and THF is tetrahydrofuran, crystallizes with two independent half-anion units [one Ni atom is at the centre of symmetry ({1/2}, {1/2}, 0) and the other is at the centre of symmetry ({1/2},0, {1/2})], one cation unit (located in a general position) and one THF solvent molecule in the asymmetric unit. The crystal structure consists of two-dimensional layers composed of parallel mixed chains, where pairs of cations alternate with single anions. These layers are separated by sheets of anions and THF molecules.