A mixed-valence Keggin-structural 12-molybdophosphoric acid hydrate, NH4(C4N2H12)(C2N2H10)2 [Mo 4 V Mo 8 VI PO40]·2H2O (1), has been synthesized hydrothermally and characterized by single-crystal X-ray diffraction, elemental analysis, TG, XRD, IR, Raman, UV–Vis diffuse reflection spectrum and XPS spectrum. The compound 1 crystallizes in the monoclinic system with cell parameters of a = 20.668(4) Å, b = 10.827(2) Å, c = 21.508(4) Å, β = 117.070(3)°, V = 4,285.6(14) Å3, and space group C 2/c, Z = 4 at 293 K. The final full-matrix least-squares refinement converged to R 1 = 0.029 for the observed reflections (4,721) with I > 2σ(I) and wR 2 = 0.065 for all data (4,837) and S = 1.048. Compared with another compound, (C4N2H12)(C2N2H10)2[Mo5P2O23] (2) (Chen et al., Chin J Struct Chem 30:1178, 2011), compound 1 was obtained via only changing molar ratio of reactants and the pH value of reaction system. Meanwhile, compound 1 contains the same two kinds of organonitrogen ligands, even their molar ratio, but entirely different space architecture and distinct heteropoly blue building block, [Mo 4 V Mo 8 VI PO40]7−. The crystal packing of 1 presents interesting 1D Zig-zag, 2D laminated and even 3D honeycomb-like configurations.