A novel compound [H-IDP](4)[PMo12O40]center dot 8H(2)O 1 based on Keggin-type phosphormolybdate has been synthesized by hydrothermal method and characterized by IR spectroscopy, elemental analyses and single-crystal X-ray diffraction. The composite crystallizes in the monoclinic system, space group C2/m with a = 13.937(5), b = 27.033(5), c = 10.857(5) angstrom, beta = 122.489(5)degrees, V = 3450(2) angstrom(3), Mr = 2611.11, Z = 2, Dc = 2.498 g/cm(3), F(000) = 2486, mu = 2.243 mm(-1), the final R = 0.0568 and wR = 0.1216 for 2707 observed reflections with I > 2 sigma(I). X-ray structural study shows that 1 consists of a [PMo12O40](4-) polyanion, four protonated IDP cations and eight H2O molecules. In the structure of 1, a 3D network forms by hydrogen bond of [PMo12O40](4-) polyanion, HIDP+ cation and H2O molecules. Upon excitation wavelength of 280 nm in hydroxylic solvents at room temperature, 1 shows fluorescence property.