Optical signal circuits can realize ultimately efficient signal processing. Optical micro-resonators, which can localize light at certain spots, are important parts in terms of achieving the circuits. From the perspective of absorption rates, single-crystal calcium fluoride (CaF2) is the most suitable material for highly efficient optical micro-resonators, and ultra-precision cylindrical turning (UPCT) is a feasible fabrication process for CaF2 optical-micro resonators. However, CaF2 is characterized by brittleness and crystal anisotropy; therefore, it is necessary to prevent micro-cracks in UPCT because such cracks would lead to light scattering and resonator performance deteriorations. In this study, rectangular optical micro-resonators are manufactured by UPCT, and the influence that micro-cracks have on resonator performance is experimentally investigated.