Metanatroautunite, Na[(UO2)(PO4)](H2O)3, from the Lake Boga granite, Victoria, Australia, has tetragonal symmetry, space group P4/ncc, with the unit-cell parameters: a = 6.9935(7), c = 17.5101(12) Å, V = 856.40(13) Å3, and Z = 4. The crystal structure has been solved and refined to R1 = 0.0398 for 368 unique reflections [F > 4σ(F)] and 0.0456 for all 496 unique reflections. Metanatroautunite has an almost identical corrugated polyhedral sheet to meta-autunite-group minerals, consisting of corner-sharing uranyl square pyramids and phosphate tetrahedra. Hydrogen bonds (and cation-oxygen bonds) link the water molecules in the interlayer into square-planar sets, which are connected together creating 8-membered arrays. Metanatroautunite is identical to synthetic Na[(UO2)(PO4)](H2O)3.