Mirror-surface machining is very important machining technology to manufacture optical parts, especially brittle materials. In case of optical plastics, it is produced through both grinding and polishing till now. New machining method which is more efficient and contributed to the protection of the environmental pollution is, therefore, studied. In this study, experimental results and an analysis of surface roughness in ultrasonic vibration cutting of optical plastics(CR-39) which is used for optical lens are presented. In results, a comparison of the micro-structure of machined surface produced by cutting with ultrasonic vibration and conventional turning is presented by analyzing S.E.M. photograph. Also, wavelength spectrum analysis is performed to investigate the surface-characteristics machined by ultrasonic vibration cutting.