The diversity of Assimineidae in China is poorly known. Populations historically identified as Assiminea violacea Heude, 1882 are reevaluated based on extensive material from the Changjiang Estuary and Zhoushan. Morphological examination of shells, radulae, and reproductive anatomy confirms that A. violacea is a junior synonym of Assiminea grayana Fleming, 1828. Molecular analyses of a 557 bp COI fragment support this revision, with phylogenetic reconstructions revealing a well-supported monophyletic clade comprising both Chinese and European specimens. This study provides the first confirmed record of A. grayana in China and discusses its potential introduction via maritime transport. These findings resolve a long-standing taxonomic confusion and clarify the biogeographic history of the genus in the Northwest Pacific.