A study was made to locate artificial reef accurately using the echo sounder. The bottom buoy unit grouped polyethylene floators with 14, 18 and 30 cm in diameter, and was shot around the artificial reef area off the shore in Keelung. Sounding experiments were executed using an echo sounder (type: HE-301) from March to December, 1989. This study obtained the following conclusions: The bigger the floator of bottom bouy was, the stronger and closer to the theoretical value of idealized perfectly reflecting sphere its target strength was; The bottom buoy unit was able to be detected clearly by any normal echo sounder used in current. Furthmore, it was an accurate and simple method for locating artifical reef; Concrete anchors were used to provide enough holding power for maintaining the bottom buoy unit on station. However, nylon rope used for mooring lines was more easily broken than chain in bad weather conditions.