Self-floating corner reflectors of which mechanical strength and accuracy are maintained by use of polystyrene foam, light in weight and transparent to microwaves, as medium among reflecting surfaces of metallic foil are trially manufactured and tested. The results are reported here. The weight is only 440g and able to float on the sea surface without any devices. The main characters are equal to ordinary corner reflectors without any perceptible losses due to polystyrene foam medium.