The title compound, disodium dimanganese(II) tris-[ortho-molybdate(VI)], was prepared by solid-state reactions. The structure can be described as being composed of Mn2Mo2O14 double-chains that are inter-connected by corner-sharing with MoO4 tetra-hedra, leading to a three-dimensional framework with channels propagating in [100] and [001] in which the Na(+) counter-cations are located. One of these Na sites is located on an inversion centre, one is partially occupied [occupancy 0.341 (9)], and one is statistically occupied by Na and Mn in a ratio of 0.829 (5):0.171 (5). Na1.67Mn2.17(MoO4)3 is isotypic with structures of the Ag2 M 2(MoO4)3 (M = Zn, Mg, Co, Mn) family. A comparative structural description is provided between the structure of the title compound and those of related phases containing (MXO8) n chains (M = Mo, Mn and X = As) or M 2O10 (M = Mo, Mn, Nb, V) dimers.