In the title compound, (C(14)H(16)N(4))(2)[Mo(8)O(26)], the β-octa-molybdate anion is centrosymmetric. N-H⋯O hydrogen bonds link the diimidazolium cations and the polyoxidoanions into a chain structure along [100]. π-π inter-actions between the imidazole rings and between the imidazole and benzene rings [centroid-centroid distances = 3.611 (2) and 3.689 (3) Å, respectively] connect the chains.