Stainless steel has a variety of engineering applications due to its superior properties. Drilling is a commonly seen machining technique for stainless steels. Rotary Ultrasonic Machining (RUM) is one of the nontraditional machining processes for brittle materials and some metals. However, there is no report on RUM of stainless steel. This paper presents the results of a designed experiment investigation into RUM of stainless steel. A three-variable two-level full factorial design was employed to reveal main effects as well as interaction effects of three process variable (spindle speed, ultrasonic power, and feedrate). The process outputs studied include cutting force and torque. Published in the Transactions of NAMRI/SME, Vol. 37, 2009, pp. 261-268.