Abstract: In order to construct a unidirectional traveling-wave ring resonator or non-planar ring resonator that utilizes the magneto-optical effect of the laser gain medium itself without additional magneto-optical crystals, so as to meet the application requirements of preparing continuous wave single-frequency 1.5 μm solid-state lasers with power greater than watts, the Verdet constants of Er, Yb : YAl₃(BO₃)₄ crystals were experimentally investigated by means of magneto-optical modulation technique combined with balanced detection. The Verdet constants of Er, Yb : YAl₃(BO₃)₄ crystals at different doped atomic fractions and temperatures were obtained. The results show that the measured Verdet constants of Er, Yb : YAl₃(BO₃)₄ crystals with different doped atomic fractions of Yb ions, namely 10%, 15% and 25%, are 48.11°/(T·m), 33.05°/(T·m) and 10.88°/(T·m), respectively. When the temperature of Er, Yb : YAl₃(BO₃)₄ crystal with a Yb³⁺ doped atomic fractions of 25% is increased from 13 ℃ to 38 ℃, the Verdet constant showes a nonlinear decrease from 11.40°/(T·m) to 10.15°/(T·m). The Verdet constant of the Er, Yb : YAl₃(BO₃)₄ crystal is comparable with that of the yttrium aluminum garnet crystal. Moreover, the crystal exhibits paramagnetism. The magneto-optic rotation performance of the gain medium can be improved by either employing the low doped crystal or lowering the crystal temperature. This study provides a reference for the construction of continuous wave single frequency solid-state lasers without additional magneto-optical crystals.