The crystal structure of the completely sodium ion exchanged phase of a-zirconium phosphate, Zr2(NaPO4)4.6H2O, has been determined by using X-ray powder diffraction data. The partial structural model for the full-pattern refinement was derived from a combination of direct methods and heavy atom methods. The crystals belong to the triclinic space group P1 with a = 8.9192(3) angstrom, b = 10.5824(4) angstrom, c = 5.4045(3) angstrom, alpha = 94.238(3)-degrees beta = 90.164(4)-degrees, gamma = 111.013(3)-degrees, and Z = 1. The final agreement factors are R(p) = 0.101, R(wp) = 0.135, and RF = 0.037. The layer structure is similar to that of the parent a-zirconium phosphate in terms of metal coordination and bridging nature of the phosphate group. The complete exchange of the protons in the parent compound, Zr(HPO4)2-H2O, affected the arrangement of the layers sufficiently to lower the symmetry from monoclinic to triclinic. The sodium ions are surrounded by oxygen atoms of both the water molecules and the phosphate groups. Electron diffraction studies show superlattice points along the smallest axis, which is not apparent in the powder diffraction data.