The influence of aluminum doping on the ionic conductivities and phase transition in the La2Mo2-xAlxO 9-δ(x = 0.1, 0.2, 0.3) oxide-ion conductors has been investigated by XRD, DSC and dielectric relaxation measurements. The results indicate that the solubility of Al3+ in La2Mo 2O9sample is about 10mol%, Al3+ can not suppress the α/βphase transition in the La2Mo2O 9, and the aluminum substituted La2Mo2O 9 has a higher conductivity in whole temperature than that of pure La2Mo2O9. ©(2012) Trans Tech Publications.