In this article, isocyanate was adopted to modify Y(2)O(3 )powder for the purpose of preparing transparent Y(2)O(3 )ceramics via gel casting. The modification could enhance the hydration resistance of Y(2)O(3 )powder through the steric hindrance effect. The coating mechanism can be proved by the infrared spectrum of the surface-modified Y2O3 powder. Modification could not only prevent Y2O3 particles from reacting with water, but also prevents agglomeration between particles. The viscosity of the slurry with a solid content of 52.7 vol% is only 0.48 Pa center dot s at the shear rate of 100 s(-1), which is suitable for preparing high-density compacts by gel casting. The transmittance of the sample (1840 degrees C x 8 h, 1 mm thickness) at 1100 nm reaches 75%. The microstructure of the sintered body is dense with the average grain size of 6.5 mu m without obvious impurities nor pores. Five mol% ZrO2-doped Y2O3 transparent ceramic fairing with the diameter of 5 cm without defects was successfully fabricated by gel casting (52.7 vol% solid volume) and vacuum sintering (1840 degrees C x 8 h).