A practical high tetravalent Zr4+ ion conducting solid, Zr1-x/4TaP3-xWxO12 (0.0 <= x <= 0.2), was successfully prepared by strictly selecting both a crystal structure and constituent ion species. By introducing the hexavalent W6+ as the constituent ion of NASICON-type structure, the tetravalent Zr4+ ion conductivity was greatly enhanced in comparison with that of ZrTa(PO4)(3) because of the reduction of the electrostatic interactions between the mobile Zr4+ cations and surrounding O2- anions as well as the expansion of the NASICON crystal lattice. Among the samples prepared, the Zr39/40TaP2.9W0.1O12 (x = 0.1) solid showed the highest Zr4+ ion conductivity of 4.7 x 10(-4) S center dot cm(-1) at 873 K which enters into the practical application range (> 10(-4) S center dot cm(-1)).