A tetra-n-butylammonium (TBA) salt of [Ta10O28](6-) was synthesized by heating TBA(6)[H2Ta6O19] in toluene for a prolonged period. X-ray structural analysis of TBA(6)[Ta10O28]center dot 6H(2)O revealed that the anion has the decametalate structure and is isostructural with the decavanadate and decaniobate anions [a = 15.8517(8) angstrom, b = 19.364(1) angstrom, c = 21.935(1) angstrom, beta = 93.638(1)degrees, V = 6719.4(6) angstrom(3), Z = 2, and space group P2(1)/n at 292(2) K].