An optical isolator using Tb<sup>3+</sup>-rich magneto-optical glass was demonstrated. We successfully developed a glass having a large Faraday effect, whose Verdet constant was 60 rad/T m at 1064 nm, ~1.6 times that of Tb<sub>3</sub>Ga<sub>5</sub>O<sub>12</sub> crystal (TGG). The glass was also highly transparent in the visible―near-IR region. An optical isolator operating at a wavelength of 1064 nm was developed using the glass, whose isolation was over 33 dB and insertion loss was under 0.2 dB. The size of the magnet could be reduced, and consequently, a small (51 × 40 × 40 mm<sup>3</sup>) optical isolator was realized.