Single crystals of the title compound, {Na(4)[Mo(VI)O(2)(SO(4))(3)]}(n), were grown from a melt of MoO(3) and Na(2)SO(4) in Na(2)S(2)O(7). In contrast to the structure of the isoformular K compound, K(4)[Mo(VI)O(2)(SO(4))(3)], with its monomeric anion, this sodium analogue contains a polymeric anion of the type {[Mo(VI)O(2)(SO(4))(2)-μ-(SO(4))](4-)}(n). The Mo(VI) cations, surrounded by two tightly bonded O atoms and four O atoms of one bridging and two terminal sulfato ligands, form zigzag chains parallel to [100]. All four Na(+) cations are situated between the anionic chains and have distorted octa-hedral coordination spheres.