The phase structure plays an important role on the transmittance of zirconia ceramics. In this paper, 3 mol% Y2O3-stabilized ZrO2 (3YSZ) and 5 mol% Y2O3-stablized ZrO2 (5YSZ) were prepared, and sintered at 1450℃, 1500℃ and 1550℃ respectively. The phase structure and constitution of the specimens were characterized by XRD, SEM and EMPA. And the transmittance of the specimens was tested by UV-Vis spectrophotometer in the visible range. The relationship between the phase structure and the transmittance is discussed. The results reveal that 3YSZ and 5YSZ both have a binary assemblage of t and t′ phases, while more t phase was found in the 3YSZ, and more t′ phase was found in 5YSZ, the content of which increase with the sintering temperature seperately. The transmittance of 5YSZ is higher than that of 3YSZ in the visible light range. Concerning the phase structures and the transmittance of 3YSZ and 5YSZ, the conclusion that the transmittance of t′ phase is higher than that of t phase is brought forth.