We have developed a new three-dimensional (3D) endoscopic ultrasound system (EUS) with convex scanning echoendoscope to diagnose and navigate for endoscopic puncture using the 3D image. To detect the position of the probe and to monitor the shape of the scope inside the body, we use a fiber optic tracking system which is shaped like a ribbon (Shapetape, Measurand Inc.). The fiber optic tracking system could measure bend and twist at each position of the ribbon The position of the tip of the echoendoscope is allotted to a 2D image, and the system can reconstruct and visualize a 3D image in real-time. We have reported results of our experimental studies and animal studies.