In an exposure test, wharf roach (Ligia exotica Roux) was exposed to perfluorooctane sulfonate (PFOS )via diet (0.1 mg/g-diet) for 2 days. 1 day after cessation of exposure, concentration of PFOS was increased to 1019 ± 144 ng/g-wet and still detected to 377 ± 321 ng/g-wet at 12 days after the exposure. Biological half-life of PFOS in wharf roach was estimated to be 11.9 days. In a field study, wharf roach were collected from 14 coastal sites in Japan. PFOS were detected from each one individual in Tsuyazaki, Fukuoka Pref. (215 ng/g-dry) and Taira, Nagasaki Pref. (601 ng/g-dry). These results suggested that wharf roach could be a promised biomonitoring species for PFOS in coastal area.