Single crystals of the title compound, {Na4[MoVIO2(SO4)3]}n, were grown from a melt of MoO3 and Na2SO4 in Na2S2O7. In contrast to the structure of the isoformular K compound, K4[MoVIO2(SO4)3], with its monomeric anion, this sodium analogue contains a polymeric anion of the type {[MoVIO2(SO4)2--(SO4)]4}n. The MoVI 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 octahedral coordination spheres.