The molybdovanadogermanic heteropoly acid H5GeMo11VO40. 24H(2)O was prepared for the first time by the stepwise acidification and the stepwise addition of solutions of the component elements, The optimal proportion of the component compounds and the pH of the synthesis reaction are given. The product was characterized by means of inductively coupled plasma (ICP), potentiometric titration, IR, UV, V-51 NMR, powder X-ray diffraction, and thermal analysis. The results of ac impedance measurement show that its proton conductivity is 2.03 x 10(-4) s.cm(-1) at 18 degrees C and the activation energy for proton conduction is 39.74 kJ/mol.