Scratch tests were conducted using a standard pyramid indenter against alpha-SiAlON ceramics with different microstructures: (i) fine equiaxed grains and (ii) large elongated grains. The formation and propagation of cracks were investigated via focused ion-beam milling, with an emphasis on the effect of microstructure on material removal. The fine equiaxed microstructure exhibited high resistance to material removal at low loads, because of its high hardness and homogeneous structure. As the load increased, radial and lateral cracks developed, resulting in large-scale chipping. In contrast, the large elongated microstructure showed a propensity to form micro-cracks and microabrasion, which is characteristic of partial grain removal, at low loads. With increasing loads, however, the large elongated grains suppressed the propagation of radial and lateral cracks, and, consequently, no large-scale chipping occurred. Implications for material design in abrasive-wear conditions have been discussed.