Optical grade D y 2 O 3 ceramics was successfully produced by adding a small amount of Z r O 2 as a sintering aid and hot isostatic pressing treatment at 1500 ∘ C after pre-sintering at 1550 ∘ C . No residual pores, grain boundary phases, or second phases were detected inside the transparent ceramics. Since birefringence was not observed under the polarizer, the produced D y 2 O 3 ceramics is an optically isotropic body. There was almost no beam distortion during the laser irradiation test, and the optical loss was extremely small ( < 0.1 % / c m ). The Verdet constant was 422 r a d T − 1 m − 1 at a wavelength of 633 nm, and the extinction ratio was 34 dB.