The temperature dependence of the ionic conductivity of (1 - x)ZrO2-(x - y)Sc2O3-yYb(2)O(3) (x = 0.07-0.15, y = 0.00-0.03) was examined to clarify the origins of the ionic conductivity decrease at low temperature. For y = 0.02-0.03 in this system, the cubic phase was stabilized at room temperature and discontinuity in the ionic conductivity disappears. The Arrhenius plots of the ionic conductivity for the stabilized samples were curved. The grain boundary resistance for (1 - x)ZrO2-(x - 0.03)Sc2O3-0.03Yb(2)O(3) (x = 0.07-0.15) was separated from the total resistance with the AC impedance method. This allowed us to conclude that grain boundary resistance is not the cause of the curvature in the Arrhenius plots for this system.