By reaction of [As2W19O67(H2O)](14-), NiCl2 center dot 6H(2)O, and phen under hydrothermal conditions, a new organic-inorganic tungstoarsenate hybrid [Ni(phen)(3)](4)[As2W18O60]{[Ni(phen)(2)][H2As2W18O60]}center dot 12H(2)O (where phen = 1,10-phenanthroline) (1) was obtained via self-assembly and characterized by elemental analysis, infrared (IR) spectroscopy, solid UV-vis absorption spectrum, and single-crystal X-ray diffraction (XRD). An unprecedented 18-tungstoarsenate Dawson cluster, beta-[W18O54(AsO3)(2)](6-), encapsulating two pyramidal arsenite AsO33- anions as templates and exhibiting interesting intramolecular As center dot center dot center dot As interaction is first achieved. 1 displays a one-dimensional (1D) chain architecture constructed by alternating beta-[W18O54(AsO3)(2)](6-) and nickel(II) complexes [Ni(phen)(2))](2+). The resulting hybrid can act as a photocatalyst to prompt the degradation of Rhodamine B (RhB) with excellent efficiency.