To identify the ionic conductivity mechanism of Nb+5-substituted La2Mo2O9, an ion dynamic study on these substituted materials has been performed. Although the ionic conductivity and mechanism of conduction has already been reported, the ion dynamic study of these materials has scarcely been carried out to establish the conduction mechanism. The frequency dependence of ac conductivity of Nb+5-doped La2Mo2O9 has been explained by means of frequency dispersion of conductivity as well as in terms of modulus formalism. The values of the exponential parameter s of the universal dielectric response and the stretching exponent beta of the Kohlrausch-Williams-Watts relation are evaluated from curve fitting. Temperature dependence of such parameters is checked and is interpreted for the plausible mechanism of ionic motion in the material at low temperature. The scaling behavior of these materials are also studied to evaluate the composition and temperature dependence of the conduction mechanism. (C) 2009 The Electrochemical Society. [DOI: 10.1149/1.3129437] All rights reserved.