A new method using ultrasonic-assisted chemical machining for producing very fine rods has been proposed. Basic theory for chemical machining of a cylindrical copper workpiece in a ferric chloride solution has been introduced to predict the machining rate, and the relationship between its diameter and time has been derived from a model of the reaction. Experiments showed that the diameter decreased non-linearly with time as the theory predicted. The ultrasonic agitation not only accelerated the material removal rate uniformly, but also produced smooth surfaces of fine rods.