Indium molybdate and eutectic composites (1 – х)In2(MoO4)3–хMoO3 (where the molar fraction is х = 0; 0.1; 0.3; 0.5) were synthesized, their conductivity has been studied as a function of the temperature and oxygen pressure in the gas phase. The ion transport numbers were determined by the Tubandt method. In2(MoO4)3 is shown to be an ionic conductor, the main charge carrier being the molybdate ion, \({\text{MoO}}_{4}^{{2 - }}.\) No composite effect is found in the In2(MoO4)3–MoO3 system: at 600°С the conductivity of the composites (1 ‒ х)In2(MoO4)3–хMoO3 does not depend on the MoO3 content. The absence of the composite effect is likely to be due to the negative thermal expansion coefficient of In2(MoO4)3, which prevents the formation of a highly conductive continuous film at the In2(MoO4)3/MoO3 interface.