The structure of the title compound, NH(4)(C(8)H(20)N)(3)[Mo(8)O(26)], is built up by discrete cations and anions, with two formula units in the asymmetric unit. The β-octa-molybdate anions are linked to the ammonium cations via N-H⋯O hydrogen bonding involving terminal oxide groups and to the tetra-ethyl-ammonium cations via weak C-H⋯O inter-actions.