We report on the mid-infrared laser operation of a cubic 15 at.% Er3+:KY3F10 crystal. In the quasi-continuous-wave regime, the peak power reaches 255 mW at 2.80 µm (the 4I11/2→4I13/2 transition) with a slope efficiency of 10.9% and a laser threshold of 58 mW. Two pumping schemes (to the 4I11/2 and 4I9/2 states) are compared. The emission properties of the Er3+ ions in KY3F10 are studied, indicating high stimulated-emission cross-section of 0.57×10-20cm2 at 2.80 µm, a large gain bandwidth of 40 nm, and a long 4I11/2 state lifetime of 4.64 ms.