The reducibility of oxide-ion conductors La2-xBaxMo2-yWyO9-delta, (x = 0, 0.06: y = 0, 0.1, 0.5, 1.0) and La(2)Mo(1.9)A(0.1)O(9-delta) (A = Al, Ga) were studied in the reducing atmosphere of 5%H-2 + Ar by means of impedance spectroscopy measurement. The introduction of Ba at La site in La2Mo2-yWyO9 can lower the sintering temperature by about 100 K in comparison with the La2Mo2-yWyO9 samples. All substitutions can enhance the conductivity and improve the reducibility in the temperature range from 548 to 923 K. The double substitution of Ba and W as well as substitution of Al or Ga at Mo sites has a better stabilizing effect than the single tungsten substitution. Among these substitutions the introduction of Al has the best stabilizing effect. (C) 2008 Elsevier Ltd. All rights reserved.