Crystals of Na-Pb-O and Na-Pb-Bi-O were electrosynthesized on the anode from molten salts. The resulting crystals have a hexagonal structure, in which the base ions (Pb and Bi) are in high oxidation states. By using KOH/NaOH (atomic ratio K:Na=1:1) mixture as a flux, incorporation of K ions into the lattice is inhibited while incorporation of Bi ions is enhanced. The magnetic measurement shows that the Na-Pb-Bi-O crystals are dominated by diamagnetism. Crystals of Na-Pb-O and Na-Pb-Bi-O were electrosynthesized on the anode from molten salts. The resulting crystals have a hexagonal structure, in which the base ions (Pb and Bi) are in high oxidation states. KOH / NaOH (atomic ratio K: Na = 1: 1) mixture as a flux, incorporation of K ions into the lattice is inhibited while incorporation of Bi ions is enhanced. The magnetic measurement shows that the Na-Pb-Bi-O crystals are dominated by diamagnetism.