Laser oscillation at a wavelength of 1520 nm was obtained in an Er:Yb:YAl(3)(BO(3))(4) crystal end pumped by a 970 nm diode laser. Under the absorbed pump power of 14.6 W, quasi-continuous-wave output powers of 1.1 W with slope efficiency of 13% and 0.8 W with slope efficiency of 11% were achieved in hemispherical and plano-plano cavities, respectively. The laser spectra were recorded for both cavities. The influence of the thermal load in the crystal on the 1520 nm laser oscillation was analyzed.