Currently, the finishing process depends on hand lapping so far which requires high labor cost. This paper introduces a novel ultra-precision finishing method for an artificial knee joint by means of abrasive waterjet. The proposed method is as follows. Ultra fine abrasive particles are mixed in water of a machining chamber in which a workpiece is positioned under a spindle. High pressured waterjet is injected under the water to the workpiece in a tangential manner at a machining point. Abrasive particles gather around the machining point. The proposed method can realize utilization of ultra fine particles which is very difficult in conventional manner. Furthermore, it is advantageous from the viewpoints of nozzle wear and abrasive particle reuse as well as process automation. Then, the proposed finishing method is applied to the workpiece with free form shape. A nozzle motion and the position of a workpiece are planed by CAD data of the workpiece. By applying this finishing method to finishing for an artificial knee joint, good surface of an artificial knee joint is obtained.