Milling is one of the discontinuous machining methods which makes tools contact with workpiece continuously along with the regular change of shear force. Providing strong materials for fabricating the required pieces challenge machining and producing complex shapes. Therefore, operations intended for reducing machining forces as well as increasing the final surface smoothness are remarkably important of which using ultrasonic vibrations is one method. This study centers on ultrasonic vibration-assisted milling operation. The required ultrasonic vibrations are applied using a transducer to an AISI 1045 steel workpiece and a 7075 aluminum. Also, by using an arithmetic modal analysis simulation on the related workpiece and fixture, the designing process was performed in a way to equate the natural frequency of the whole set to that of the ultrasonic transducer. The resonant frequency obtained for the steel and aluminum workpieces was 19840 and 19757[Formula: see text]Hz, respectively, and the milling operation was done by applying ultrasonic vibrations to the workpiece. The results obtained from surface roughness measurement indicated that an increase in the ultrasonic intensity from 15[Formula: see text]W/cm2 to 22.5[Formula: see text]W/cm2 in the aluminum workpiece resulted in improved surface roughness ([Formula: see text] by 70%. In addition, an increase in the ultrasonic intensity from 15[Formula: see text]W/cm2 to 22.5[Formula: see text]W/cm2 improved the surface smoothness ([Formula: see text] by 72%. Moreover, concerning the steel workpiece while the tool is perpendicular to the direction ahead of the workpiece, it was clear that applying 22.5[Formula: see text]W/cm2 ultrasonic vibrations to the end-milled surfaces resulted in an approximate increase in the average and maximum surface smoothness by 53% and 45%, respectively. Furthermore, applying 30[Formula: see text]W/cm2 ultrasonic vibrations to face-milled surfaces, either perpendicular to or parallel to the tool, led to an approximate increase in the average and maximum surface smoothness by 35% and 25%, respectively.