The electronic structures of undoped c- and t-ZrO2 were calculated by a first-principles molecular orbital method. A preliminary analysis revealed that experimental energy-loss near-edge structure profiles obtained in ZrO2-8 mol% Y2O3 could be satisfactorily explained from the present theoretical calculation. The calculation suggests that the stability of t-ZrO2 could be described by the interaction between neighboring oxygen ions rather than the covalency of Zr-O bonds. The effect of dopant cations on the stability of cubic-zirconia solid solutions can be estimated semiquantitatively in terms of the repulsive Coulomb force between neighboring oxygen ions.