Composite materials (1 - f)SrWO4-fSiO(2) and (1 - f)BaWO4-fSiO(2), where f is the volume fraction of the disperse additive SiO2, are prepared by the solid-phase method and studied by the XRD, TG-DSC, and SEM-EDX methods. The conductivity of composites is measured by the electrochemical impedance method as a function of temperature, partial pressure of oxygen in the gas phase, and composition. The contribution of the ionic conductivity was assessed based on the sum of transport numbers of ions measured by the EMF method. It is shown that the addition of 20-25 vol % nano-SiO2 to the low-conducting oxygen-ion conductors SrWO4 and BaWO4 leads to the 20 and 12-fold increase in the conductivity of composites. The increase in the conductivity in these systems is explained by the additional contribution of interphase boundaries formed between the MeWO4 matrix and dispersoid nanoparticles.