In a mangrove tidal flat of Iriomote Island, Okinawa, an experiment on utilization of empty gastropod shells by hermit crabs was carried out. One hundred twenty-seven gastropod shells of Terebralia palustris were left at the mangrove tidal flat in the Funaura Bay of the Iriomote Island. After 48 hours, these shells were re-collected and shell size and distance from an experimental point were measured. Thirty-five shells were utilized by hermit crabs. Sixty shells were not used and left as before. Most of the shells used by the hermit crabs were collected at the distance of less than 10m from the experimental point. The most moved shells by the hermit crab were too far distance of 120m from the experimental point. The small-sized shells used by hermit crabs were collected near the experimental point. But, the shells collected at a distant from the experimental point were only large ones. In the mangrove swamp, dead gastropod shells were used by the hermit crabs immediately after death and they moved the shells to a long distance on a short time.