In this work, the advantages and drawbacks of Ultrasonic Assisted Turning (UAT) have been investigated focusing on the effect of tool vibration on surface quality. Several experiments have been performed on mild steels changing the cutting speed, feed and depth of cut, to study how the influence of the ultrasonic vibration on the surface roughness varies depending on the cutting conditions. The results obtained show that the ultrasonic vibration can improve the surface quality. The authors also propose a new booster design based on the theory of longitudinal vibration of a bar with varying cross-sectional area for a higher amplification of the ultrasonic vibration.