Composite materials Sm2(WO4)3-WO3 were prepared by the solid state method and their transport properties have been examined by the electrochemical impedance technique and conductivity measurements versus oxygen partial pressure. It was shown that heterogeneous doping of the oxygen ion conductor Sm2(WO4)3 with a semiconductor WO3 even at low concentration of WO3 (volume fraction f < 0.13) led to an increase in ionic conductivity of the composites by more than an order of magnitude. This effect is caused by formation of the non-autonomous interface phase Sm2W6O21 covering grain boundaries of Sm2(WO4)3. At high concentrations of WO3 (f > 0.13) the composite materials comprise biphasic mixture with mixed ionic-electronic conductivity. Dependences of the conductivity on temperature, WO3 concentration and oxygen partial pressure were described in terms of the brick-wall model (at f < 0.13) and the generalized mixing equation (at f > 0.13) and conductivity parameters of the O2− ion conducting interface phase were determined. © 2023