The genus Assiminea (Gastropoda: Assimineidae) are amphibious, brackish snails that inhabit moist areas near marine or non-marine water bodies. Here, eleven specimens of Assiminea grayana are collected from river estuaries and the intertidal to supratidal zones of the western and southern seas of the Korean Peninsula. It is the first record of Assiminea grayana J. Fleming, 1828 in the Korean fauna. To verify the species identification, we examined its ecological characteristics, morphological features and DNA barcoding, which consistently supported the existance of A. grayana in Korea. This species has 6-7 slightly swollen whorls, impressive suture, and sharpened apex. The angle of the aperture acute was adapical. The blackish cephalic tentacles form short, rounded lobes each with eyes at the tip, and their gray snout is divided into two parts. Its COI sequence showed 99.7% similarity to those of individuals from the UK and Germany. The ML tree showed a close relationship of A. grayana from Korea and Europe, which formed a sister group with A. hiradoensis and A. estuarina exclusively inhabiting Northeastern Asia. It is likely to imply that A. grayana might be originated from Northestern Asia. Further studies integrating morphological and molecular data are essential for clarifying the taxonomic status and migration histories of A. grayana and related species.