This paper deals with the precision NURBS interpolator for wire-EDM. Previous research about OAC (Open Architecture Controller) is mostly aimed at NC cutting machines such as milling or lathes, and hence these results are inadequate to apply to wire-EDM. In contradiction to NC machines, wire-EDM operates relatively slow feed rates and based on a feedback control loop to the machining process. The 2-stage interpolation method which reflects wire-EDM specific characteristics was proposed. The constant interpolation error could be acquired through 1 st stage interpolation. Feed rate regulation was performed through 2nd stage interpolation. The suggested algorithm was implemented to test-bed PC-NC system. Computer simulations and the experimental machining were conducted.