Silicotunostic acid crystal hydrates H4SiW12O40 . nH(2)O (n = 1-27) have been studied using impedance and vibrational spectroscopy, thermal analysis, and X-ray powder diffraction. Essentially differing proton hydrate complex species correspond to different n. Proton conductivity a has been measured. The conductivity is found to be a function of the amount of crystal water and of the type of proton hydrate complex.