Сomplex oxides La2Mo2O9 and La2Mo3O12 were obtained by conventional solid-state reaction method. The { 0.9 La2Mo2O9- 0.1 La2Mo3O12} composite was obtained by mechanical mixing of components. The phase composition of products was monitored by means of X-ray phase analysis. Transport properties, thermodynamic stability of matrix and composite samples were investigated. It has been established that introduction of an inert heterogeneous dopant La2Mo3O12, contributes to increase in conductivity of composite by 6-10 times relative to matrix sample, a decrease in the activation energy of conductivity, and an increase in the stability of ceramics at low partial oxygen pressures. However, it doesn`t suppress structural phase transition α-La2Mo2O9→β-La2Mo2O9. The growth effect in conductivity of composite may be associated with partial stabilization of high-symmetry β-form La2Mo2O9 at low temperatures. The calculated activation energies of conductivity Ea for La2Mo2O9 are 0.62 and 1.18 eV, respectively, at high and low temperatures. Values of Ea are 0.53 and 1.12 eV, respectively, for composite. La2Mo2O9 is an ionic conductor in a wide range of oxygen partial pressures of 10-18-0.21 atm, contribution of electronic conductivity is absent up to 10-20 atm for composite.