A large number of the set-nets are set in Namhaedo coast of Korea. The floats of these set-nets are not only small even in case of large floats but also they scarcely have distinguishable marks such as light buoys or flags, so that they are very hard to be recognized by naked eyes and thus became probable obstacles to navigation for the passing ships and the fishing vessels. In order to research the capability of detecting such nets with Radar, the author investigated a maximum detectable range of the ordinarly large floatsand of a floating corner reflectors of various size and shape by Radar. The results obtained are as follows; 1. A maximum detectable range of large floats at a close range can be calculated by the Radar equation in sufficient accuracy. 2. Large floats of the large set-nets are also detectable by Radar even though it's detectable range boundary was within 0.2-0.65 miles. And the Radar picture of large floats was easier to be found with somewhat higher setting of the gain control on shorter range scale of the 1 mile. 3. Floating corner reflector rather suitable for set-net floats of "S" type reflector proposed in this paper, of which the dimension must be above 17cm in diameter to be detectable by Radar at 2 miles.t 2 miles.