The de conductivities of ZrO2-Y2O3 ceramic alloys (in the range 3-12 mol% of Y2O3) have been obtained from ac impedance measurements at temperatures between 250 degrees and 370 degrees C, The Almond-West ac conductivity model has been applied to evaluate hopping rates in this system, The migration enthalpies mere evaluated and shown to increase with yttria concentration, but all values determined were shown to be lower than the corresponding activation enthalpies for conductivity. The association enthalpies thus calculated mere shown to be very small in 3 mol% Y2O3-ZrO3 and to increase with yttria concentration until the yttria contents were high enough to form fully stabilized cubic zirconia, For these samples the association enthalpies are about 0.19 eV, and no longer sensitive to yttria content. The low hopping rate at high yttria concentration might be attributed to low entropy in the system, which might be attributed to the formation of vacancy clusters and/or an ordering of the structure.