A new compound with a cubic structure, (Ba0.05K0.95)BiO3. l/6H(2)O (BKBO), was synthesized by electrochemical crystal growth using a rotating anode in molten KOH flux at 255 degrees C. The BKBO crystal had the KSbO3 structure and belonged to space group Im (3) over bar (No. 204) with Z = 12. Refinement of X-ray diffraction data at room temperature gave a = 10.0204(2) Angstrom, V = 1006.1(1) Angstrom(3), and R = 2.4% for 1465 unique reflections. Potassium, barium, and hydrated oxygen were found to occupy different sites in the tunnel structure. The electrical conductivity at room temperature was similar to the ionic conductor KBiO3. BKBO decomposed to Bi2O3, K2O, and BaO above 400 degrees C.