The optical properties and microstructure are evaluated for a transparent cubic (8 mol% yttria-stabilized) zirconia (c-YSZ) prepared by high-pressure spark plasma sintering. Oxygen vacancies and residual pores are primary defects in the present transparent c-YSZ, and the combination influence of these two defects determines the optical properties. The as-sintered transparent zirconia strongly absorbs the incident light due to the formation of high concentration of oxygen vacancies. Annealing treatment in oxidizing atmosphere can improve the transparency by reducing oxygen defects. The existence of fine pores in the present zirconia causes scattering of the incident light.