The eight-nickel-capped polyoxoazonickelate, [Ni-20(OH)(24)-(MMT)(12)(SO4)](NO3)(2)center dot 6H(2)O (1; MMT = 2-mercapto-5-methyl-1,3,4-thiadiazole), has been synthesized, which has an alpha-Keggin structure with eight nickel caps. In this structure, the polyatom is the late transition metal Ni-II; the central heteroatom is S, and the organic terminal ligand becomes the primary part of the Keggin structure. This is a Keplerate-type cluster which shows a central Ni-12(II) cuboctahedron formed by the 12 Ni-II centers of the classical alpha-Keggin core and a Ni-8(II) hexahedron formed by the eight nickel caps.