An Asian species of Perinereis, which has been regarded as a local population of a cosmopolitan species P. cultrifera (Grube, 1840) (type locality: Italy), is described as a new species, P. euiini., based on Korean specimens. This new species is distinguishable from P. cultrifera and other similar species such as P. floridana (Ehlers, 1868) (type locality: USA), P. anderssoni Kinberg, 1866 (type locality: Brazil), and P. helleri (Grube, 1878) (type locality: Philippines) by the character combination of the absence of lateral group of paragnaths in area III on the proboscis, the presence of small notopodial prechaetal lobe in anterior parapodia, and the greatly expanded dorsal ligule in posterior parapodia. All previous records of “P. cultrifera” from eastern Asia (Taiwan, China, Japan, and Korea) are judged to belong to P. euiini sp. nov., leading to the conclusion that P. cultrifera is not a cosmopolitan species. Specimens previously identified as P. cultrifera var. floridana (or P. cultrifera floridana) in eastern Asia are also judged to belong to P. euiini sp. nov., although they have different paragnath number in area V (one instead of three). Their aberrant paragnath number was regarded as an intraspecific variation of P. euiini sp. nov. The comparison of DNA sequences of the mitochondrial cytochrome c oxidase subunit I (COI) between P. euiini sp. nov. and “P. cultrifera” from China and Portugal also supports the erection of the new species.