The differences between CO1 sequences of our mytilus samples and those of Mytilus galloprovincialis from South America, Kanagawa in Japan, North Atlantic, Auckland in New Zealand, and Hobart in Australia range from 1.4% to 5.9%. However, CO1 sequences of our sample are different from that of mytilus edulis by 15% ~ 21% and that of mytilus corscus by 21% ~ 23%. The molecular phylogenetic tree reconstruted strongly support that all 4 individuals are Mytilus galloprovincialis. However, none of our sample grouped together with the clade of Mytilus edulis. These results show that introduced mytilus species in Korea sea waters is Mytilus galloprovincialis, not Mytilus edulis. It is also evident that some aquacultered mytilus species are also Mytilus galloprovincialis, not Mytilus corscus.