During the expedition of the Zoological Institute of the Russian Academy of Sciences (ZIN RAS) in 1998, a fossil impression of a polychaete worm belonging to the family Nephtyidae Grube, 1850, containing fragments of jaws, was found in the west of Sakhalin. The find is dated to the Middle and Upper Miocene. There are no published records of any finds of fossil nephtyids in the area. Based on the analysis of the jaw shape, it is concluded that the nephtyid impression may belong to the genus Nephtys Cuvier 1817 or the genus Aglaophamus Kinberg, 1865.