The ionic conductivity of substituted PbWO4 phase was investigated by electrochemical methods. A substitution method by samarium, as shown in Pb1-xSmxWO4+x/2, to intend to increase the concentration of interstitial oxide ions enhanced the ionic conductivity. The charge carrier in the substituted phase was the oxide ion. The conductivity behavior due to the oxide ion was almost the same as the previously reported La-substituted phase. The relation between the conductivity and the crystal parameters in the substituted phases were also discussed.