The grinding and polishing behaviour of three tailored α-sialon microstructures made of the same chemical composition: fine-grained, bimodal and large elongated-grained, were determined. The fine-grained microstructure was characterised by extensive lateral cracks in the grinding process and widespread grain pullout during the mechanical polishing; in contrast, the large elongated-grained microstructure exhibited high grinding damage resistance, and a defect-free, mirror-like surface after mechanical polishing. The bimodal microstructure showed an intermediate behaviour during both processes. The material removal mechanisms during grinding and polishing were analysed and modelled as a function of grain size and aspect ratio.