A collection of 35 oyster samples from Nangan and Beigan intertidal coasts of Matsu, Taiwan was conducted in June 2009. Sequencing of the partial cytochrome oxidase c subunit I gene (COI) revealed that 4 of 35 specimens were Kumamoto oyster Crassostrea sikamea (Amemiya, 1928). This study provides the first evidence of C. sikamea in Matsu, Taiwan, as a new record that expanded southernmost geographical distribution of the present species. We compared the difference between C. sikamea from Matsu and Kyushu, Japan, and provided specimen photos and an identification key for further research.