Oxide ion conductivity of the pure and aliovalent ion substituted rare-earth pyrohafnates in the series RE2-xSrxHf2O7 and RE2Hf2-xAlxO7 (RE = Gd and Nd; x = 0-0.2) has been explored in the temperature range 400 degrees C-700 degrees C for the first time. It is seen that, conductivity is enhanced by doping 5 atom% Sr at the rare-earth site in these systems. Well defined impedance plots due to grain interior and grain boundary resistances were obtained in the Gd pyrohafnate with Sr substitution. The results of the conductivity variation for the pure, Sr and Al doped phases are explained on the basis of pyrochlore structure.