Ligia exotica Roux is an amphibious arthropod abundantly inhabiting sea-shores of Honshu, Shikoku and Kyushu in Japan. Here we present a detailed distribution map of the isopod on lagoon-shores of Lake Shinjiko in Shimane Prefecture. A total of 113 areas on Lake Shinji and Ohashi River was surveyed from July to September in 1995. The isopod was found in the most areas surveyed, whereas absent in areas at the western part of Lake Shinji where influx of fresh water by Hii River dominated. Hence, salinity of water lapping their habitat should be a plausible factor delimiting the distribution there.