Approximately 12.2% of the adult population has experienced overactive bladder (OAB) in Korea. Sacral nerve stimulation (SNS) is an effective treatment for controlling intractable symptoms of OAB. Its problem with uncer-tainty of needle insertion, however, is one of difficult problems. The purpose of this thesis was to develop a needle-based navigation system for SNS. Skin-to-target path and real-time instrument guidance were provided by the de-signed software interface based on pre-operative the 3D model from 1.25 mm CT data slices. Using an electromag-netic navigation device, instrumented 18 g needles were inserted into the target position in a dummy. The registra-tion error between the CT coordinate and the electromagnetic tracking coordinate was 0.87mm in the dummy, and seven nonexperts operated for 10 attempts on each subject. And conventional operation method was also tested by same nonexperts. Two methods were tested to compare the accuracy assessment. The mean distance between the instrument tip position and the center of the target in a virtual environment was 2.9±1.3 mm (n=70) in the navigation system, 8.7±4.1 mm (n=70) in the conventional operation method. The developed navigation system allows the instrument insertion into the target position. Also the system allows less experienced operators to insert the instrument as well.