As SOFC technology relies at present on La-based perovskites as cathode materials, we have analyzed the effect La-incorporation might have in the ionic conductivity of P-Gd2Zr2O7, a pyrochlore-type fast oxygen ion conductor. Single phase powder samples with different La/Gd ratio, were prepared in the pyrochlore-type Gd2-yLayZr2O7 solid solution (0 <= y <= 1) by mechanically milling stoichiometric mixtures of the corresponding oxides. Electrical conductivity measurements were performed for different compositions by using pressed pellets sintered at 1500 degrees C, as a function of frequency and temperature. Despite of increasing structural ordering (decreasing number of mobile charge carriers), it was found that oxide-ion conduction at intermediate temperatures is almost La-content independent for y <= 0.8 because of decreasing dc activation energy (from 1.13 to 0.85 eV). We show that these results can be explained in terms of weaker ion-ion interactions in better ordered structures (i.e., rich La-content), highlighting the importance of structural ordering/disordering in determining the dynamics of mobile oxygen ions. (C) 2008 Elsevier B.V. All rights reserved.