The material removal mechanism in microcutting of ceramics is analysed based on the fracture mechanics. An algorithm for the application of the linear fracture mechanics concept is first described, and according to the algorithm the material removal mechanism in orthogonal microcutting of a sintered alumina is then elucidated in terms of crack behavior. Also, in-situ scanning electron microscope observation is conducted in order to determine the dynamic behaviour of cracks during microcutting process. It is found that two types of crack play significant roles in the material removal mechanism. A crack forms near the tip of the cutting edge of the tool at the beginning of the process, and it grows forward and downward along the minimum principal stress direction as the process advances. After a certain growth, the crack is arrested, and another crack forms and propagates upward to the free surface from the cutting edge along the maximum shear stress direction. As the result, the primary crack remains behinds on the machined surface as a residual crack.