The purpose of this paper is to reveal material removal mechanisms of optical fiber end-surface in lapping processes. The lapping process experiments are conducted using fixed diamond abrasive lapping films with various particle sizes of , , , and . The micrographs of the optical fiber end-surfaces are observed using a scanning electron microscope. The experimental results show that there exist three material removal modes in the lapping processes: brittle fracture mode, semibrittle and semiductile mode, and ductile mode. These modes are mainly controlled by abrasive particle size, and there appears a brittle-ductile transition’s critical point when lapping films with a particle size of are used to lap optical fiber end-surfaces. An interpretation is proposed for the formation mechanism of the plastic deformed layer on the optical fiber end-surfaces.