Mirror-surface machining is a very important technology to manufacture precision parts, especially optical parts. So far, those are produced by multi-processes, i.e. grinding and polishing, which are inefficient. In this study, the ultrasonic vibration cutting as a substitute for them for the precision machining of optical plastics (CR-39) which have been used for optical lens is suggested and experimented. To analyze the characteristics of surfaces machined by the ultrasonic vibration cutting in the ductile mode, the wavelength spectrum analysis is carried out and the micro-structure is compared with that of a conventional cutting. As a result, in micro cutting by the ultrasonic vibration, it was confirmed that the surfaces of ductile cutting is obtained in depth of cut less than 2.7㎛.