It is an object of the present invention to provide a magneto-optical material containing as a main component an oxide that includes a terbium oxide and having a large Verdet constant at a wavelength in the 1.06 μm region (0.9 to 1.1 μm) and high transparency, and to provide a small-sized optical isolator suitably used in a fiber laser for a processing machine. The magneto-optical material of the present invention contains an oxide represented by Formula (I), TbxR1−x)2O3, where x satisfies 0.4≦×≦1.0 and R includes at least one element selected from the group consisting of scandium, yttrium, and lanthanoid elements other than terbium, at a content of at least 99 wt %.