In this paper, high quality cutting of 1 mm dense Al2O3 electronic ceramic processed by a fiber laser with spot diameter of 15 μm was reported. The narrow kerf with 30μm width was obtained with laser power of 100 W. 300 W is the laser power threshold of the kerf enlargement. Under higher laser power, the ceramics can be damage-free cut with higher cutting speed. Striation-free cutting could be achieved at 1000 W laser power with a cutting speed of 350 mm/s. The ratio of cutting speed to laser power for striation-free cutting was determined as 0.35. The black cutting surface was due to the mass tetragonal alumina induced by N2 as assist gas.