New bismuth oxides, ABi(2)O(6), (A = Mg, Zn) with the trirutile-type structure were prepared by low-temperature hydrothermal reaction using NaBiO3 . nH(2)O as a starting material. The tetragonal lattice parameters are a = 4.8260(1) and c = 9.7190(1) Angstrom for A = Mg and a = 4.8386(1) and c = 9.7422(3) Angstrom for A = Zn. The crystal structure of MgBi2O6 was refined using neutron diffraction data giving final R factors of R-WP = 12.6 and R-P = 9.64%. Both bismuth oxides decomposed by reduction of Bi5+ to Bi3+ above 380 degrees C.