Two new pentavalent bismuthates, CaBi₂O_6−x·1.1H₂O and PbBi₂O_6−x·H₂O were prepared from NaBiO₃·nH₂O. Broadened X-ray powder diffraction patterns for both bismuthates were indexed to the hexagonal cell observed for PbSb₂O₆-type SrBi₂O₆. The lattice parameters were a = 0.555(1) and c = 0.530(1) nm for CaBi₂O_6−x·1.1H₂O and a = 0.5544(4) and c = 0.531(1) nm for PbBi₂O_6−x·H₂O. At elevated temperatures, the Ca derivative decomposed to Ca₃Bi₈O₁₅ and an unknown phase via the fluorite-type structure, whereas the Pb derivative changed to Pb_1/3Bi_2/3O_4/3 via the fluorite-type (Pb_1/3Bi_2/3)O_1.4. Both Ca and Pb derivatives exhibited photocatalytic activity for the decomposition of phenol under visible light irradiation, although the adsorption of phenol was observed under dark conditions. The fluorite-type phases evolved from the Ca and Pb derivatives did not adsorb phenol under dark conditions, and their photocatalytic activities toward phenol decomposition under visible light were inferior to those of the parent compounds.