The novel polyoxometalate [H2PW9Ni4O34(OH)(3)(H2O)(6)](2-) (1) has been synthesized and characterized by IR spectroscopy, polarography, elemental analysis, and magnetic measurements. An X-ray single-crystal analysis was carried out on Cs-2[H2PW9Ni4O34(OH)(3)(H2O)(6)]. 5H(2)O, which crystallizes in the orthorhombic system, space group Pbcn, with a = 24.3131(3) Angstrom, b = 21.5400(1) Angstrom, 19.8936(3) Angstrom, V = 10418.4(2) Angstrom(3), Z = 8, and rho(calcd) = 3.767 g/cm(3). Structural analysis based on 14 734 independent reflections leads to a solution, R = 8.04% (1 > 2 sigma(I)). Anion 1 consists of a Ni4O4 cubane fragment which is inserted into a trivacant lacunary B-alpha-[PW9O34](9-) Keggin unit. Magnetic measurements show that the Ni-Ni exchange interactions are ferromagnetic.