The synthesis and molecular structure of a dimeric aluminium complex composed of tri-lacunary α-Keggin polyoxometalate is described. The polyoxometalate, K(6)Na[(A-PW(9)O(34))(2){W(OH)(OH(2))}{Al(OH)(OH(2))}{Al(μ-OH)(OH(2))(2)}(2)]·19H(2)O (KNa-1), afforded by the reaction in water of a tri-lacunary Keggin polyoxotungstate with excess aluminium nitrate, followed by crystallization from water, was obtained as analytically pure, homogeneous, colorless crystals. The compound KNa-1 was characterized by elemental analysis, TG/DTA, FT-IR, solution NMR ((31)P, (27)Al, and (183)W), and X-ray crystallography. The single-crystal X-ray structure analysis revealed that two 6-coordinate aluminium ions linked with two bridging hydroxyl groups and four water molecules, i.e., [Al(III)(2)(μ-OH)(2)(OH(2))(4)](4+); a unit of a 6-coordinate tungsten ion linked with a hydroxyl group and a water molecule, i.e., [W(OH)(OH(2))](5+); a unit of a 6-coordinate aluminium ion linked with a hydroxyl group and a water molecule, i.e., [Al(OH)(OH(2))](2+), were sandwiched between two tri-lacunary α-Keggin polyoxotungstates, resulting in an overall C(s) symmetry.