Electrical conductivities, sigma, of (Zr1-xCexO2)(0.9)(CaO)(0.1) (x = 0.1-1.0) were investigated by a D.C. four terminal technique at 1173-1573 K as a function of the oxygen partial pressure from 10(-15) to 1 atm. In the region of x = 0.4-1.0, the electrical conductivity is separated into the ionic and electronic conductivity by using the relation of sigma = sigma (ion) + sigma (0)(e) P-O2(-1/4). The electrical conduction at Po, = I atm is essentially ionic. The composition dependence of the electronic conductivity shows opposite tendency to that of the ionic conductivity, that is, the electronic conductivities increase with the increase in CeO2 content (x) and show a maximum at x similar or equal to 0.6, then decrease with x while the ionic conductivity behaves vice versa, In the CaO doped ZrO2-CeO2 system, the formation of the solid solution results in the low ionic and high electronic conduction.