A new Percophidid fish was found in Tachi harbor, north eastern Taiwan. Osopsaron formosensis n. sp. is characterized by dorsal iris flap, maxillary with spine, anterior nostril tubular, 5 dorsal spines, fast three very elongate, 20-22 dorsal rays, 24-27 branched anal rays and 8 or 9 branched caudal rays.