To obtain the smooth surface of an etched-fiber core and to precisely control the diameter of the etched-fiber, an ultrasonic etching system was developed. The effect of ultrasonic power and temperature on the etch rate of fibers (fiber cladding and fiber core) and the surface morphology of etched-fibers were investigated in the 12.5 % percentage concentration of HF solution, respectively. Experimental results indicate that the etch rate is enhanced by the ultrasonic agitation, the relationship between etch rate and etching time is nonlinear and the surface roughness is increased with the etching time in the HF solution. Thereafter, the Buffered HF (BHF) solution was promoted, and the BHF solutions were prepared by making use of 12.5 % HF solution and 25 % NH4OH solution. The influence of BHF solutions on the etch rate and surface morphology was investigated. Obtained results reveal that the smooth surface of etched-fiber core and the linear relationship between etch rate and etching time can be obtained in BHF solution when V (HF): V (NH4OH) is 2, the ultrasonic power is at 165 W and the temperature at 40℃.