Cupped oysters are common and abundant along the coast of China, but their classification has been uncertain. In previous studies, we classified 2 of the cupped oysters into 2 subspecies: Crassostrea gigas gigas from the northern coast of China and Crassostrea gigas angulata from the southern coast of China. There is another small cupped oyster that seems different from these 2 species and resembles Crassostrea sikamea Amemiya 1928. To determine the taxonomic status of this oyster and its distribution, we collected wild oysters from 12 sites in China, identified putative C. sikamea with genetic markers, and compared them with known C. sikamea in both morphology and sequences of the mitochondrial 16S rRNA and cytochrome oxidase I gene fragments. Sequence analyses confirm classification based on genetic markers that this small cupped oyster from China is indeed C. sikamea. Our data show that C. sikamea not only occurs naturally in China, but also lives in abundance over a wide geographical distribution, ranging from Jiangsu to Guangxi, including Hainan Island. Our findings greatly extend the known distribution range of this species, and the extended distribution follows the Kuroshio and Tsushima currents, suggesting that ocean currents may play a role in shaping oyster distribution. Knowing the distribution range of C. sikamea is important to our understanding of its evolutionary history as well as fishery management and aquaculture breeding of this commercially important species.