Efficient 1.57 μm continuous-wave laser was demonstrated in an X-cut, 2.0 mm-thick Er3+:Yb3+:LaMgB5O10 crystal with sapphire cooling end-pumped by a 976 nm laser diode. In a plano-concave cavity, a laser with a maximum output power of 0.61 W and a slope efficiency of 23% was realized at an absorbed pump power of 4.0 W. A continuous-wave 1566 nm micro-laser with a maximum output power of 0.47 W and a slope efficiency of 16% was also obtained. The lasers were totally linear polarization parallel to the crystalline Z axis. The results show that the Er3+:Yb3+:LaMgB5O10 crystal with high thermal conductivity may be a good gain medium for laser around 1.55 μm.