The grain-boundary resistances of 9 mol% Y2O3 and 1.5 mol% Al2O3 codoped-ZrO2 after sinterings of 1520-1600 degrees C were measured by the complex impedance approach. And the microstructure of the specimen was analyzed by means of SEM, EPMA and TEM. According to a space-charge theory analysis, the space-charge potential of the Y2O3 and Al2O3-codoped ZrO2 is negative, which is the result of an Al-Zr’ segregation and V-O(..) depletion in the space-charge layers. As Al-Zr’ has a stronger tendency to form associates with V-O(..) than Y-Zr’, the Al-Zr’ segregation further reduces the concentration of mobile V-O(..) in the space-charge layers, thus increasing the grain-boundary resistance contributed from the space-charge layers. A higher V-O(..) concentration in the space-charge layers of the Al2O3/ZrO2 is suggested by the space-charge theory, but due to the pores and the amorphous phases covering the Al2O3 particles, the effect of the space-charge layers with high V-O(..) concentration will not be very obvious.