Composites of (1 – x)Al2(WO4)3–xWO3 and (1 – x)Al2(WO4)3–xAl2O3 are synthesized and their conductivity is studied as dependent on the temperature and oxygen pressure in the gas phase. The transport numbers of charge carriers are determined using the EMF and Tubandt methods. It is shown that there is a composite effect in the Al2(WO4)3–Al2O3 system: when 20–60 mol % of nanodispersed Al2O3 is added to Al2(WO4)3, ionic conductivity of the composites increases by 0.5–0.8 orders of magnitude as compared to Al2(WO4)3. The dependence of conductivity of the (1 – x)Al2(WO4)3–xAl2O3 composites on the Al2O3 content passes through a maximum. Such an effect is typical for composite solid electrolytes and can be explained by an additional contribution of interfaces, where the complex oxide is more disordered. There is no composite effect in the Al2(WO4)3–WO3 system. When Al2(WO4)3 and WO3 are mixed, a statistical composite is formed with its conductivity determined by the conductivity of the main phase.